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GitHub - Naetw/CTF-pwn-tips: Here record some tips about pwn. Something is obsoleted and won't be updated. Sorry about that.
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flex-justify-between flex-items-center d-block d-lg-flex flex-lg-nowrap flex-lg-items-center js-details-container js-header-menu-item"> <button type="button" class="HeaderMenu-link border-0 width-full width-lg-auto px-0 px-lg-2 py-lg-2 no-wrap d-flex flex-items-center flex-justify-between js-details-target" aria-expanded="false"> Product <svg opacity="0.5" aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-chevron-down HeaderMenu-icon ml-1"> <path d="M12.78 5.22a.749.749 0 0 1 0 1.06l-4.25 4.25a.749.749 0 0 1-1.06 0L3.22 6.28a.749.749 0 1 1 1.06-1.06L8 8.939l3.72-3.719a.749.749 0 0 1 1.06 0Z"></path> </svg> </button> <div class="HeaderMenu-dropdown dropdown-menu rounded m-0 p-0 pt-2 pt-lg-4 position-relative position-lg-absolute left-0 left-lg-n3 pb-2 pb-lg-4 d-lg-flex flex-wrap dropdown-menu-wide"> <div class="HeaderMenu-column px-lg-4 border-lg-right mb-4 mb-lg-0 pr-lg-7"> <div class="border-bottom pb-3 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0 .368-.014.733-.052 1.086.23.462.477 1.088.644 1.517 1.258.364 2.233 1.721 2.605 2.656a.832.832 0 0 1 .053.22v2.869a.641.641 0 0 1-.078.256ZM12.172 11h-.344a4.323 4.323 0 0 1-.355.508C10.703 12.455 9.555 13 7.965 13c-1.725 0-2.989-.359-3.782-1.259a2.005 2.005 0 0 1-.085-.104L4 11.741v6.585c1.435.779 4.514 2.179 8 2.179 3.486 0 6.565-1.4 8-2.179v-6.585l-.098-.104s-.033.045-.085.104c-.793.9-2.057 1.259-3.782 1.259-1.59 0-2.738-.545-3.508-1.492a4.323 4.323 0 0 1-.355-.508h-.016.016Zm.641-2.935c.136 1.057.403 1.913.878 2.497.442.544 1.134.938 2.344.938 1.573 0 2.292-.337 2.657-.751.384-.435.558-1.15.558-2.361 0-1.14-.243-1.847-.705-2.319-.477-.488-1.319-.862-2.824-1.025-1.487-.161-2.192.138-2.533.529-.269.307-.437.808-.438 1.578v.021c0 .265.021.562.063.893Zm-1.626 0c.042-.331.063-.628.063-.894v-.02c-.001-.77-.169-1.271-.438-1.578-.341-.391-1.046-.69-2.533-.529-1.505.163-2.347.537-2.824 1.025-.462.472-.705 1.179-.705 2.319 0 1.211.175 1.926.558 2.361.365.414 1.084.751 2.657.751 1.21 0 1.902-.394 2.344-.938.475-.584.742-1.44.878-2.497Z"></path><path d="M14.5 14.25a1 1 0 0 1 1 1v2a1 1 0 0 1-2 0v-2a1 1 0 0 1 1-1Zm-5 0a1 1 0 0 1 1 1v2a1 1 0 0 1-2 0v-2a1 1 0 0 1 1-1Z"></path> </svg> <div> <div class="color-fg-default h4">GitHub Copilot</div> Write better code with AI </div> </a></li> <li> <a class="HeaderMenu-dropdown-link d-block no-underline position-relative py-2 Link--secondary d-flex flex-items-center Link--has-description pb-lg-3" data-analytics-event="{"location":"navbar","action":"security","context":"product","tag":"link","label":"security_link_product_navbar"}" href="https://github.com/features/security"> <svg aria-hidden="true" height="24" viewBox="0 0 24 24" version="1.1" width="24" data-view-component="true" class="octicon octicon-shield-check color-fg-subtle mr-3"> <path d="M16.53 9.78a.75.75 0 0 0-1.06-1.06L11 13.19l-1.97-1.97a.75.75 0 0 0-1.06 1.06l2.5 2.5a.75.75 0 0 0 1.06 0l5-5Z"></path><path d="m12.54.637 8.25 2.675A1.75 1.75 0 0 1 22 4.976V10c0 6.19-3.771 10.704-9.401 12.83a1.704 1.704 0 0 1-1.198 0C5.77 20.705 2 16.19 2 10V4.976c0-.758.489-1.43 1.21-1.664L11.46.637a1.748 1.748 0 0 1 1.08 0Zm-.617 1.426-8.25 2.676a.249.249 0 0 0-.173.237V10c0 5.46 3.28 9.483 8.43 11.426a.199.199 0 0 0 .14 0C17.22 19.483 20.5 15.461 20.5 10V4.976a.25.25 0 0 0-.173-.237l-8.25-2.676a.253.253 0 0 0-.154 0Z"></path> </svg> <div> <div class="color-fg-default h4">Security</div> Find and fix vulnerabilities </div> </a></li> <li> <a class="HeaderMenu-dropdown-link d-block no-underline position-relative py-2 Link--secondary d-flex flex-items-center Link--has-description pb-lg-3" data-analytics-event="{"location":"navbar","action":"actions","context":"product","tag":"link","label":"actions_link_product_navbar"}" href="https://github.com/features/actions"> <svg aria-hidden="true" height="24" viewBox="0 0 24 24" version="1.1" width="24" data-view-component="true" class="octicon octicon-workflow color-fg-subtle mr-3"> <path d="M1 3a2 2 0 0 1 2-2h6.5a2 2 0 0 1 2 2v6.5a2 2 0 0 1-2 2H7v4.063C7 16.355 7.644 17 8.438 17H12.5v-2.5a2 2 0 0 1 2-2H21a2 2 0 0 1 2 2V21a2 2 0 0 1-2 2h-6.5a2 2 0 0 1-2-2v-2.5H8.437A2.939 2.939 0 0 1 5.5 15.562V11.5H3a2 2 0 0 1-2-2Zm2-.5a.5.5 0 0 0-.5.5v6.5a.5.5 0 0 0 .5.5h6.5a.5.5 0 0 0 .5-.5V3a.5.5 0 0 0-.5-.5ZM14.5 14a.5.5 0 0 0-.5.5V21a.5.5 0 0 0 .5.5H21a.5.5 0 0 0 .5-.5v-6.5a.5.5 0 0 0-.5-.5Z"></path> </svg> <div> <div class="color-fg-default h4">Actions</div> Automate any workflow </div> </a></li> <li> <a class="HeaderMenu-dropdown-link d-block no-underline position-relative py-2 Link--secondary d-flex flex-items-center Link--has-description pb-lg-3" data-analytics-event="{"location":"navbar","action":"codespaces","context":"product","tag":"link","label":"codespaces_link_product_navbar"}" href="https://github.com/features/codespaces"> <svg aria-hidden="true" height="24" viewBox="0 0 24 24" version="1.1" width="24" data-view-component="true" class="octicon octicon-codespaces color-fg-subtle mr-3"> <path d="M3.5 3.75C3.5 2.784 4.284 2 5.25 2h13.5c.966 0 1.75.784 1.75 1.75v7.5A1.75 1.75 0 0 1 18.75 13H5.25a1.75 1.75 0 0 1-1.75-1.75Zm-2 12c0-.966.784-1.75 1.75-1.75h17.5c.966 0 1.75.784 1.75 1.75v4a1.75 1.75 0 0 1-1.75 1.75H3.25a1.75 1.75 0 0 1-1.75-1.75ZM5.25 3.5a.25.25 0 0 0-.25.25v7.5c0 .138.112.25.25.25h13.5a.25.25 0 0 0 .25-.25v-7.5a.25.25 0 0 0-.25-.25Zm-2 12a.25.25 0 0 0-.25.25v4c0 .138.112.25.25.25h17.5a.25.25 0 0 0 .25-.25v-4a.25.25 0 0 0-.25-.25Z"></path><path d="M10 17.75a.75.75 0 0 1 .75-.75h6.5a.75.75 0 0 1 0 1.5h-6.5a.75.75 0 0 1-.75-.75Zm-4 0a.75.75 0 0 1 .75-.75h.5a.75.75 0 0 1 0 1.5h-.5a.75.75 0 0 1-.75-.75Z"></path> </svg> <div> <div class="color-fg-default h4">Codespaces</div> Instant dev environments </div> </a></li> <li> <a class="HeaderMenu-dropdown-link d-block no-underline position-relative py-2 Link--secondary d-flex flex-items-center Link--has-description pb-lg-3" 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20H10.75A1.75 1.75 0 0 1 9 18.25v-1.465a.75.75 0 0 1 1.5 0v1.465c0 .138.112.25.25.25h5.5a.75.75 0 0 1 .53.22l2.72 2.72v-2.19a.75.75 0 0 1 .75-.75h2a.25.25 0 0 0 .25-.25v-9.5Z"></path> </svg> <div> <div class="color-fg-default h4">Discussions</div> Collaborate outside of code </div> </a></li> <li> <a class="HeaderMenu-dropdown-link d-block no-underline position-relative py-2 Link--secondary d-flex flex-items-center Link--has-description" data-analytics-event="{"location":"navbar","action":"code_search","context":"product","tag":"link","label":"code_search_link_product_navbar"}" href="https://github.com/features/code-search"> <svg aria-hidden="true" height="24" viewBox="0 0 24 24" version="1.1" width="24" data-view-component="true" class="octicon octicon-code-square color-fg-subtle mr-3"> <path d="M10.3 8.24a.75.75 0 0 1-.04 1.06L7.352 12l2.908 2.7a.75.75 0 1 1-1.02 1.1l-3.5-3.25a.75.75 0 0 1 0-1.1l3.5-3.25a.75.75 0 0 1 1.06.04Zm3.44 1.06a.75.75 0 1 1 1.02-1.1l3.5 3.25a.75.75 0 0 1 0 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id="validation-62108d00-21b1-4953-a765-62ca992c3455" hidden="hidden"> <span class="FormControl-inlineValidation--visual"> <svg aria-hidden="true" height="12" viewBox="0 0 12 12" version="1.1" width="12" data-view-component="true" class="octicon octicon-alert-fill"> <path d="M4.855.708c.5-.896 1.79-.896 2.29 0l4.675 8.351a1.312 1.312 0 0 1-1.146 1.954H1.33A1.313 1.313 0 0 1 .183 9.058ZM7 7V3H5v4Zm-1 3a1 1 0 1 0 0-2 1 1 0 0 0 0 2Z"></path> </svg> </span> <span></span> </div> </div> <div data-target="query-builder.screenReaderFeedback" aria-live="polite" aria-atomic="true" class="sr-only"></div> </query-builder></form> <div class="d-flex flex-row color-fg-muted px-3 text-small color-bg-default search-feedback-prompt"> <a target="_blank" href="https://docs.github.com/search-github/github-code-search/understanding-github-code-search-syntax" data-view-component="true" class="Link color-fg-accent text-normal ml-2">Search syntax tips</a> <div class="d-flex flex-1"></div> </div> </div> </div> </div> </modal-dialog></div> </div> <div data-action="click:qbsearch-input#retract" class="dark-backdrop position-fixed" hidden data-target="qbsearch-input.darkBackdrop"></div> <div class="color-fg-default"> <dialog-helper> <dialog data-target="qbsearch-input.feedbackDialog" data-action="close:qbsearch-input#handleDialogClose cancel:qbsearch-input#handleDialogClose" id="feedback-dialog" aria-modal="true" aria-labelledby="feedback-dialog-title" aria-describedby="feedback-dialog-description" data-view-component="true" class="Overlay Overlay-whenNarrow Overlay--size-medium Overlay--motion-scaleFade Overlay--disableScroll"> <div data-view-component="true" class="Overlay-header"> <div class="Overlay-headerContentWrap"> <div class="Overlay-titleWrap"> <h1 class="Overlay-title " id="feedback-dialog-title"> Provide feedback </h1> </div> <div class="Overlay-actionWrap"> <button data-close-dialog-id="feedback-dialog" aria-label="Close" type="button" data-view-component="true" class="close-button 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seriously.</p> <textarea name="feedback" class="form-control width-full mb-2" style="height: 120px" id="feedback"></textarea> <input name="include_email" id="include_email" aria-label="Include my email address so I can be contacted" class="form-control mr-2" type="checkbox"> <label for="include_email" style="font-weight: normal">Include my email address so I can be contacted</label> </form></div> </scrollable-region> <div data-view-component="true" class="Overlay-footer Overlay-footer--alignEnd"> <button data-close-dialog-id="feedback-dialog" type="button" data-view-component="true" class="btn"> Cancel </button> <button form="code-search-feedback-form" data-action="click:qbsearch-input#submitFeedback" type="submit" data-view-component="true" class="btn-primary btn"> Submit feedback </button> </div> </dialog></dialog-helper> <custom-scopes data-target="qbsearch-input.customScopesManager"> <dialog-helper> <dialog data-target="custom-scopes.customScopesModalDialog" data-action="close:qbsearch-input#handleDialogClose cancel:qbsearch-input#handleDialogClose" id="custom-scopes-dialog" aria-modal="true" aria-labelledby="custom-scopes-dialog-title" aria-describedby="custom-scopes-dialog-description" data-view-component="true" class="Overlay Overlay-whenNarrow Overlay--size-medium Overlay--motion-scaleFade Overlay--disableScroll"> <div data-view-component="true" class="Overlay-header Overlay-header--divided"> <div class="Overlay-headerContentWrap"> <div class="Overlay-titleWrap"> <h1 class="Overlay-title " id="custom-scopes-dialog-title"> Saved searches </h1> <h2 id="custom-scopes-dialog-description" class="Overlay-description">Use saved searches to filter your results more quickly</h2> </div> <div class="Overlay-actionWrap"> <button data-close-dialog-id="custom-scopes-dialog" aria-label="Close" type="button" data-view-component="true" class="close-button Overlay-closeButton"><svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-x"> <path d="M3.72 3.72a.75.75 0 0 1 1.06 0L8 6.94l3.22-3.22a.749.749 0 0 1 1.275.326.749.749 0 0 1-.215.734L9.06 8l3.22 3.22a.749.749 0 0 1-.326 1.275.749.749 0 0 1-.734-.215L8 9.06l-3.22 3.22a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042L6.94 8 3.72 4.78a.75.75 0 0 1 0-1.06Z"></path> </svg></button> </div> </div> </div> <scrollable-region data-labelled-by="custom-scopes-dialog-title"> <div data-view-component="true" class="Overlay-body"> <div data-target="custom-scopes.customScopesModalDialogFlash"></div> <div hidden class="create-custom-scope-form" data-target="custom-scopes.createCustomScopeForm"> <!-- '"` --><!-- </textarea></xmp> --></option></form><form id="custom-scopes-dialog-form" data-turbo="false" action="/search/custom_scopes" accept-charset="UTF-8" method="post"><input type="hidden" data-csrf="true" name="authenticity_token" value="bJ9z/0WaeG8y4i6ONjqhqb4ryP+aIYdHXMJF6r3vVl+jNGFtBUTKeXCl2Q3Bo8VbtpQY2iQpnMtdZ58HFQU0ZA==" /> <div data-target="custom-scopes.customScopesModalDialogFlash"></div> <input type="hidden" id="custom_scope_id" name="custom_scope_id" data-target="custom-scopes.customScopesIdField"> <div class="form-group"> <label for="custom_scope_name">Name</label> <auto-check src="/search/custom_scopes/check_name" required only-validate-on-blur="false"> <input type="text" name="custom_scope_name" id="custom_scope_name" data-target="custom-scopes.customScopesNameField" class="form-control" autocomplete="off" placeholder="github-ruby" required maxlength="50"> <input type="hidden" data-csrf="true" value="v3bj37SdBL3UwlGYccGClYFMVuWY8L6FmcZxL/uQ+UeuGsxrdsxaneVggn+qW5O/B69BR3MHVs4/bnkQ5nT0BA==" /> </auto-check> </div> <div class="form-group"> <label for="custom_scope_query">Query</label> <input type="text" name="custom_scope_query" id="custom_scope_query" data-target="custom-scopes.customScopesQueryField" class="form-control" autocomplete="off" placeholder="(repo:mona/a OR repo:mona/b) AND lang:python" required maxlength="500"> </div> <p class="text-small color-fg-muted"> To see all available qualifiers, see our <a class="Link--inTextBlock" href="https://docs.github.com/search-github/github-code-search/understanding-github-code-search-syntax">documentation</a>. </p> </form> </div> <div data-target="custom-scopes.manageCustomScopesForm"> <div data-target="custom-scopes.list"></div> </div> </div> </scrollable-region> <div data-view-component="true" class="Overlay-footer Overlay-footer--alignEnd Overlay-footer--divided"> <button data-action="click:custom-scopes#customScopesCancel" type="button" data-view-component="true" class="btn"> Cancel </button> <button form="custom-scopes-dialog-form" data-action="click:custom-scopes#customScopesSubmit" data-target="custom-scopes.customScopesSubmitButton" type="submit" data-view-component="true" class="btn-primary btn"> Create saved search </button> 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class="application-main " data-commit-hovercards-enabled data-discussion-hovercards-enabled data-issue-and-pr-hovercards-enabled data-project-hovercards-enabled > <div itemscope itemtype="http://schema.org/SoftwareSourceCode" class=""> <main id="js-repo-pjax-container" > <div id="repository-container-header" class="pt-3 hide-full-screen" style="background-color: var(--page-header-bgColor, var(--color-page-header-bg));" data-turbo-replace> <div class="d-flex flex-nowrap flex-justify-end mb-3 px-3 px-lg-5" style="gap: 1rem;"> <div class="flex-auto min-width-0 width-fit"> <div class=" d-flex flex-wrap flex-items-center wb-break-word f3 text-normal"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-repo color-fg-muted mr-2"> <path d="M2 2.5A2.5 2.5 0 0 1 4.5 0h8.75a.75.75 0 0 1 .75.75v12.5a.75.75 0 0 1-.75.75h-2.5a.75.75 0 0 1 0-1.5h1.75v-2h-8a1 1 0 0 0-.714 1.7.75.75 0 1 1-1.072 1.05A2.495 2.495 0 0 1 2 11.5Zm10.5-1h-8a1 1 0 0 0-1 1v6.708A2.486 2.486 0 0 1 4.5 9h8ZM5 12.25a.25.25 0 0 1 .25-.25h3.5a.25.25 0 0 1 .25.25v3.25a.25.25 0 0 1-.4.2l-1.45-1.087a.249.249 0 0 0-.3 0L5.4 15.7a.25.25 0 0 1-.4-.2Z"></path> </svg> <span class="author flex-self-stretch" itemprop="author"> <a class="url fn" rel="author" data-hovercard-type="user" data-hovercard-url="/users/Naetw/hovercard" data-octo-click="hovercard-link-click" data-octo-dimensions="link_type:self" href="/Naetw"> Naetw </a> </span> <span class="mx-1 flex-self-stretch color-fg-muted">/</span> <strong itemprop="name" class="mr-2 flex-self-stretch"> <a data-pjax="#repo-content-pjax-container" data-turbo-frame="repo-content-turbo-frame" href="/Naetw/CTF-pwn-tips">CTF-pwn-tips</a> </strong> <span></span><span class="Label Label--secondary v-align-middle mr-1">Public</span> </div> </div> <div id="repository-details-container" class="flex-shrink-0" data-turbo-replace style="max-width: 70%;"> <ul class="pagehead-actions flex-shrink-0 d-none d-md-inline" style="padding: 2px 0;"> <li> <a href="/login?return_to=%2FNaetw%2FCTF-pwn-tips" rel="nofollow" id="repository-details-watch-button" data-hydro-click="{"event_type":"authentication.click","payload":{"location_in_page":"notification subscription menu watch","repository_id":null,"auth_type":"LOG_IN","originating_url":"https://github.com/Naetw/CTF-pwn-tips","user_id":null}}" data-hydro-click-hmac="d4ceae43ffc37e688514fc3c775118811e4b38233a17ae03df556b8523183da9" aria-label="You must be signed in to change notification settings" data-view-component="true" class="btn-sm btn"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-bell mr-2"> <path d="M8 16a2 2 0 0 0 1.985-1.75c.017-.137-.097-.25-.235-.25h-3.5c-.138 0-.252.113-.235.25A2 2 0 0 0 8 16ZM3 5a5 5 0 0 1 10 0v2.947c0 .05.015.098.042.139l1.703 2.555A1.519 1.519 0 0 1 13.482 13H2.518a1.516 1.516 0 0 1-1.263-2.36l1.703-2.554A.255.255 0 0 0 3 7.947Zm5-3.5A3.5 3.5 0 0 0 4.5 5v2.947c0 .346-.102.683-.294.97l-1.703 2.556a.017.017 0 0 0-.003.01l.001.006c0 .002.002.004.004.006l.006.004.007.001h10.964l.007-.001.006-.004.004-.006.001-.007a.017.017 0 0 0-.003-.01l-1.703-2.554a1.745 1.745 0 0 1-.294-.97V5A3.5 3.5 0 0 0 8 1.5Z"></path> </svg>Notifications </a> <tool-tip id="tooltip-8d29f3c5-1d58-48d4-ab24-10e456395f4e" for="repository-details-watch-button" popover="manual" data-direction="s" data-type="description" data-view-component="true" class="sr-only position-absolute">You must be signed in to change notification settings</tool-tip> </li> <li> <a icon="repo-forked" id="fork-button" href="/login?return_to=%2FNaetw%2FCTF-pwn-tips" rel="nofollow" data-hydro-click="{"event_type":"authentication.click","payload":{"location_in_page":"repo details fork button","repository_id":79437230,"auth_type":"LOG_IN","originating_url":"https://github.com/Naetw/CTF-pwn-tips","user_id":null}}" data-hydro-click-hmac="a7eda000115f8d1e619c51223ad26b4661fca9acf74fe057ebb7c98d510b26b5" data-view-component="true" class="btn-sm btn"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-repo-forked mr-2"> <path d="M5 5.372v.878c0 .414.336.75.75.75h4.5a.75.75 0 0 0 .75-.75v-.878a2.25 2.25 0 1 1 1.5 0v.878a2.25 2.25 0 0 1-2.25 2.25h-1.5v2.128a2.251 2.251 0 1 1-1.5 0V8.5h-1.5A2.25 2.25 0 0 1 3.5 6.25v-.878a2.25 2.25 0 1 1 1.5 0ZM5 3.25a.75.75 0 1 0-1.5 0 .75.75 0 0 0 1.5 0Zm6.75.75a.75.75 0 1 0 0-1.5.75.75 0 0 0 0 1.5Zm-3 8.75a.75.75 0 1 0-1.5 0 .75.75 0 0 0 1.5 0Z"></path> </svg>Fork <span id="repo-network-counter" data-pjax-replace="true" data-turbo-replace="true" title="231" data-view-component="true" class="Counter">231</span> </a> </li> <li> <div data-view-component="true" class="BtnGroup d-flex"> <a href="/login?return_to=%2FNaetw%2FCTF-pwn-tips" rel="nofollow" data-hydro-click="{"event_type":"authentication.click","payload":{"location_in_page":"star button","repository_id":79437230,"auth_type":"LOG_IN","originating_url":"https://github.com/Naetw/CTF-pwn-tips","user_id":null}}" data-hydro-click-hmac="d7a4a3204fb331facf9ad24b78beba18a73a30bf175bc89898d20e7884e392d5" aria-label="You must be signed in to star a repository" data-view-component="true" class="tooltipped tooltipped-sw btn-sm btn"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-star v-align-text-bottom d-inline-block mr-2"> <path d="M8 .25a.75.75 0 0 1 .673.418l1.882 3.815 4.21.612a.75.75 0 0 1 .416 1.279l-3.046 2.97.719 4.192a.751.751 0 0 1-1.088.791L8 12.347l-3.766 1.98a.75.75 0 0 1-1.088-.79l.72-4.194L.818 6.374a.75.75 0 0 1 .416-1.28l4.21-.611L7.327.668A.75.75 0 0 1 8 .25Zm0 2.445L6.615 5.5a.75.75 0 0 1-.564.41l-3.097.45 2.24 2.184a.75.75 0 0 1 .216.664l-.528 3.084 2.769-1.456a.75.75 0 0 1 .698 0l2.77 1.456-.53-3.084a.75.75 0 0 1 .216-.664l2.24-2.183-3.096-.45a.75.75 0 0 1-.564-.41L8 2.694Z"></path> </svg><span data-view-component="true" class="d-inline"> Star </span> <span id="repo-stars-counter-star" aria-label="1760 users starred this repository" data-singular-suffix="user starred this repository" data-plural-suffix="users starred this repository" data-turbo-replace="true" title="1,760" data-view-component="true" class="Counter js-social-count">1.8k</span> </a></div> </li> </ul> </div> </div> <div id="responsive-meta-container" data-turbo-replace> <div class="d-block d-md-none mb-2 px-3 px-md-4 px-lg-5"> <p class="f4 mb-3 "> Here record some tips about pwn. Something is obsoleted and won't be updated. Sorry about that. </p> <div class="mb-3"> <a class="Link--secondary no-underline mr-3" href="/Naetw/CTF-pwn-tips/stargazers"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-star mr-1"> <path d="M8 .25a.75.75 0 0 1 .673.418l1.882 3.815 4.21.612a.75.75 0 0 1 .416 1.279l-3.046 2.97.719 4.192a.751.751 0 0 1-1.088.791L8 12.347l-3.766 1.98a.75.75 0 0 1-1.088-.79l.72-4.194L.818 6.374a.75.75 0 0 1 .416-1.28l4.21-.611L7.327.668A.75.75 0 0 1 8 .25Zm0 2.445L6.615 5.5a.75.75 0 0 1-.564.41l-3.097.45 2.24 2.184a.75.75 0 0 1 .216.664l-.528 3.084 2.769-1.456a.75.75 0 0 1 .698 0l2.77 1.456-.53-3.084a.75.75 0 0 1 .216-.664l2.24-2.183-3.096-.45a.75.75 0 0 1-.564-.41L8 2.694Z"></path> </svg> <span class="text-bold">1.8k</span> stars </a> <a class="Link--secondary no-underline mr-3" href="/Naetw/CTF-pwn-tips/forks"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-repo-forked mr-1"> <path d="M5 5.372v.878c0 .414.336.75.75.75h4.5a.75.75 0 0 0 .75-.75v-.878a2.25 2.25 0 1 1 1.5 0v.878a2.25 2.25 0 0 1-2.25 2.25h-1.5v2.128a2.251 2.251 0 1 1-1.5 0V8.5h-1.5A2.25 2.25 0 0 1 3.5 6.25v-.878a2.25 2.25 0 1 1 1.5 0ZM5 3.25a.75.75 0 1 0-1.5 0 .75.75 0 0 0 1.5 0Zm6.75.75a.75.75 0 1 0 0-1.5.75.75 0 0 0 0 1.5Zm-3 8.75a.75.75 0 1 0-1.5 0 .75.75 0 0 0 1.5 0Z"></path> </svg> <span class="text-bold">231</span> forks </a> <a class="Link--secondary no-underline mr-3 d-inline-block" href="/Naetw/CTF-pwn-tips/branches"> <svg aria-hidden="true" height="16" viewBox="0 0 16 16" version="1.1" width="16" data-view-component="true" class="octicon octicon-git-branch mr-1"> <path d="M9.5 3.25a2.25 2.25 0 1 1 3 2.122V6A2.5 2.5 0 0 1 10 8.5H6a1 1 0 0 0-1 1v1.128a2.251 2.251 0 1 1-1.5 0V5.372a2.25 2.25 0 1 1 1.5 0v1.836A2.493 2.493 0 0 1 6 7h4a1 1 0 0 0 1-1v-.628A2.25 2.25 0 0 1 9.5 3.25Zm-6 0a.75.75 0 1 0 1.5 0 .75.75 0 0 0-1.5 0Zm8.25-.75a.75.75 0 1 0 0 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dir=\"auto\"\u003eCTF-pwn-tips\u003c/h1\u003e\u003ca id=\"user-content-ctf-pwn-tips\" class=\"anchor\" aria-label=\"Permalink: CTF-pwn-tips\" href=\"#ctf-pwn-tips\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch1 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eCatalog\u003c/h1\u003e\u003ca id=\"user-content-catalog\" class=\"anchor\" aria-label=\"Permalink: Catalog\" href=\"#catalog\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ca href=\"#overflow\"\u003eOverflow\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#find-string-in-gdb\"\u003eFind string in gdb\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#binary-service\"\u003eBinary Service\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#find-specific-function-offset-in-libc\"\u003eFind specific function offset in libc\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#find-binsh-or-sh-in-library\"\u003eFind '/bin/sh' or 'sh' in library\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#leak-stack-address\"\u003eLeak stack address\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#fork-problem-in-gdb\"\u003eFork problem in gdb\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#secret-of-a-mysterious-section---tls\"\u003eSecret of a mysterious section - .tls\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#predictable-rngrandom-number-generator\"\u003ePredictable RNG(Random Number Generator)\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#make-stack-executable\"\u003eMake stack executable\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#use-one-gadget-rce-instead-of-system\"\u003eUse one-gadget-RCE instead of system\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#hijack-hook-function\"\u003eHijack hook function\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#use-printf-to-trigger-malloc-and-free\"\u003eUse printf to trigger malloc and free\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"#use-execveat-to-open-a-shell\"\u003eUse execveat to open a shell\u003c/a\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eOverflow\u003c/h2\u003e\u003ca id=\"user-content-overflow\" class=\"anchor\" aria-label=\"Permalink: Overflow\" href=\"#overflow\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eAssume that: \u003ccode\u003echar buf[40]\u003c/code\u003e and \u003ccode\u003esigned int num\u003c/code\u003e\u003c/p\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003escanf\u003c/h3\u003e\u003ca id=\"user-content-scanf\" class=\"anchor\" aria-label=\"Permalink: scanf\" href=\"#scanf\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003escanf(\"%s\", buf)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003e%s\u003c/code\u003e doesn't have boundary check.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003epwnable\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003escanf(\"%39s\", buf)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003e%39s\u003c/code\u003e only takes 39 bytes from the input and puts NULL byte at the end of input.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003euseless\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003escanf(\"%40s\", buf)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eAt first sight, it seems reasonable.(seems)\u003c/li\u003e\n\u003cli\u003eIt takes \u003cstrong\u003e40 bytes\u003c/strong\u003e from input, but it also \u003cstrong\u003eputs NULL byte at the end of input.\u003c/strong\u003e\u003c/li\u003e\n\u003cli\u003eTherefore, it has \u003cstrong\u003eone-byte-overflow\u003c/strong\u003e.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003epwnable\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003escanf(\"%d\", \u0026amp;num)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eUsed with \u003ccode\u003ealloca(num)\u003c/code\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eSince \u003ccode\u003ealloca\u003c/code\u003e allocates memory from the stack frame of the caller, there is an instruction \u003ccode\u003esub esp, eax\u003c/code\u003e to achieve that.\u003c/li\u003e\n\u003cli\u003eIf we make num negative, it will have overlapped stack frame.\u003c/li\u003e\n\u003cli\u003eE.g. \u003ca href=\"https://github.com/ctfs/write-ups-2016/tree/master/seccon-ctf-quals-2016/exploit/cheer-msg-100\"\u003eSeccon CTF quals 2016 cheer_msg\u003c/a\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003cli\u003eUse num to access some data structures\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eIn most of the time, programs only check the higher bound and forget to make num unsigned.\u003c/li\u003e\n\u003cli\u003eMaking num negative may let us overwrite some important data to control the world!\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003egets\u003c/h3\u003e\u003ca id=\"user-content-gets\" class=\"anchor\" aria-label=\"Permalink: gets\" href=\"#gets\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003egets(buf)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eNo boundary check.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003epwnable\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003efgets(buf, 40, stdin)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eIt takes only \u003cstrong\u003e39 bytes\u003c/strong\u003e from the input and puts NULL byte at the end of input.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003euseless\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eread\u003c/h3\u003e\u003ca id=\"user-content-read\" class=\"anchor\" aria-label=\"Permalink: read\" href=\"#read\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003eread(stdin, buf, 40)\u003c/code\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eIt takes \u003cstrong\u003e40 bytes\u003c/strong\u003e from the input, and it doesn't put NULL byte at the end of input.\u003c/li\u003e\n\u003cli\u003eIt seems safe, but it may have \u003cstrong\u003einformation leak\u003c/strong\u003e.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eleakable\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eE.g.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003e\u003cstrong\u003ememory layout\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv class=\"snippet-clipboard-content notranslate position-relative overflow-auto\" data-snippet-clipboard-copy-content=\"0x7fffffffdd00: 0x4141414141414141 0x4141414141414141\n0x7fffffffdd10: 0x4141414141414141 0x4141414141414141\n0x7fffffffdd20: 0x4141414141414141 0x00007fffffffe1cd\"\u003e\u003cpre class=\"notranslate\"\u003e\u003ccode\u003e0x7fffffffdd00: 0x4141414141414141 0x4141414141414141\n0x7fffffffdd10: 0x4141414141414141 0x4141414141414141\n0x7fffffffdd20: 0x4141414141414141 0x00007fffffffe1cd\n\u003c/code\u003e\u003c/pre\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003eIf there is a \u003ccode\u003eprintf\u003c/code\u003e or \u003ccode\u003eputs\u003c/code\u003e used to output the buf, it will keep outputting until reaching NULL byte.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003eIn this case, we can get \u003ccode\u003e'A'*40 + '\\xcd\\xe1\\xff\\xff\\xff\\x7f'\u003c/code\u003e.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003efread(buf, 1, 40, stdin)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eAlmost the same as \u003ccode\u003eread\u003c/code\u003e.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eleakable\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003estrcpy\u003c/h3\u003e\u003ca id=\"user-content-strcpy\" class=\"anchor\" aria-label=\"Permalink: strcpy\" href=\"#strcpy\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eAssume that there is another buffer: \u003ccode\u003echar buf2[60]\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003estrcpy(buf, buf2)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eNo boundary check.\u003c/li\u003e\n\u003cli\u003eIt copies the content of buf2(until reaching NULL byte) which may be longer than \u003ccode\u003elength(buf)\u003c/code\u003e to buf.\u003c/li\u003e\n\u003cli\u003eTherefore, it may happen overflow.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003epwnable\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003estrncpy(buf, buf2, 40)\u003c/code\u003e \u0026amp;\u0026amp; \u003ccode\u003ememcpy(buf, buf2, 40)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eIt copies 40 bytes from buf2 to buf, but it won't put NULL byte at the end.\u003c/li\u003e\n\u003cli\u003eSince there is no NULL byte to terminate, it may have \u003cstrong\u003einformation leak\u003c/strong\u003e.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eleakable\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003estrcat\u003c/h3\u003e\u003ca id=\"user-content-strcat\" class=\"anchor\" aria-label=\"Permalink: strcat\" href=\"#strcat\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eAssume that there is another buffer: \u003ccode\u003echar buf2[60]\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003estrcat(buf, buf2)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eOf course, it may cause \u003cstrong\u003eoverflow\u003c/strong\u003e if \u003ccode\u003elength(buf)\u003c/code\u003e isn't large enough.\u003c/li\u003e\n\u003cli\u003eIt puts NULL byte at the end, it may cause \u003cstrong\u003eone-byte-overflow\u003c/strong\u003e.\u003c/li\u003e\n\u003cli\u003eIn some cases, we can use this NULL byte to change stack address or heap address.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003epwnable\u003c/strong\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp dir=\"auto\"\u003e\u003ccode\u003estrncat(buf, buf2, n)\u003c/code\u003e\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eAlmost the same as \u003ccode\u003estrcat\u003c/code\u003e, but with size limitation.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003epwnable\u003c/strong\u003e\u003c/li\u003e\n\u003cli\u003eE.g. \u003ca href=\"https://github.com/ctfs/write-ups-2016/tree/master/seccon-ctf-quals-2016/exploit/jmper-300\"\u003eSeccon CTF quals 2016 jmper\u003c/a\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eFind string in gdb\u003c/h2\u003e\u003ca id=\"user-content-find-string-in-gdb\" class=\"anchor\" aria-label=\"Permalink: Find string in gdb\" href=\"#find-string-in-gdb\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eIn the problem of \u003ca href=\"http://j00ru.vexillium.org/blog/24_03_15/dragons_ctf.pdf\" rel=\"nofollow\"\u003eSSP\u003c/a\u003e, we need to find out the offset between \u003ccode\u003eargv[0]\u003c/code\u003e and the input buffer.\u003c/p\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003egdb\u003c/h3\u003e\u003ca id=\"user-content-gdb\" class=\"anchor\" aria-label=\"Permalink: gdb\" href=\"#gdb\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eUse \u003ccode\u003ep/x ((char **)environ)\u003c/code\u003e in gdb, and the address of argv[0] will be the \u003ccode\u003eoutput - 0x10\u003c/code\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eE.g.\u003c/p\u003e\n\u003cdiv class=\"snippet-clipboard-content notranslate position-relative overflow-auto\" data-snippet-clipboard-copy-content=\"(gdb) p/x (char **)environ\n$9 = 0x7fffffffde38\n(gdb) x/gx 0x7fffffffde38-0x10\n0x7fffffffde28: 0x00007fffffffe1cd\n(gdb) x/s 0x00007fffffffe1cd\n0x7fffffffe1cd: \u0026quot;/home/naetw/CTF/seccon2016/check/checker\u0026quot;\"\u003e\u003cpre class=\"notranslate\"\u003e\u003ccode\u003e(gdb) p/x (char **)environ\n$9 = 0x7fffffffde38\n(gdb) x/gx 0x7fffffffde38-0x10\n0x7fffffffde28: 0x00007fffffffe1cd\n(gdb) x/s 0x00007fffffffe1cd\n0x7fffffffe1cd: \"/home/naetw/CTF/seccon2016/check/checker\"\n\u003c/code\u003e\u003c/pre\u003e\u003c/div\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003e\u003ca href=\"https://github.com/longld/peda\"\u003egdb peda\u003c/a\u003e\u003c/h3\u003e\u003ca id=\"user-content-gdb-peda\" class=\"anchor\" aria-label=\"Permalink: gdb peda\" href=\"#gdb-peda\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eUse \u003ccode\u003esearchmem \"/home/naetw/CTF/seccon2016/check/checker\"\u003c/code\u003e\u003c/li\u003e\n\u003cli\u003eThen use \u003ccode\u003esearchmem $result_address\u003c/code\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"snippet-clipboard-content notranslate position-relative overflow-auto\" data-snippet-clipboard-copy-content=\"gdb-peda$ searchmem \u0026quot;/home/naetw/CTF/seccon2016/check/checker\u0026quot;\nSearching for '/home/naetw/CTF/seccon2016/check/checker' in: None ranges\nFound 3 results, display max 3 items:\n[stack] : 0x7fffffffe1cd (\u0026quot;/home/naetw/CTF/seccon2016/check/checker\u0026quot;)\n[stack] : 0x7fffffffed7c (\u0026quot;/home/naetw/CTF/seccon2016/check/checker\u0026quot;)\n[stack] : 0x7fffffffefcf (\u0026quot;/home/naetw/CTF/seccon2016/check/checker\u0026quot;)\ngdb-peda$ searchmem 0x7fffffffe1cd\nSearching for '0x7fffffffe1cd' in: None ranges\nFound 2 results, display max 2 items:\n libc : 0x7ffff7dd33b8 --\u0026gt; 0x7fffffffe1cd (\u0026quot;/home/naetw/CTF/seccon2016/check/checker\u0026quot;)\n[stack] : 0x7fffffffde28 --\u0026gt; 0x7fffffffe1cd (\u0026quot;/home/naetw/CTF/seccon2016/check/checker\u0026quot;)\"\u003e\u003cpre class=\"notranslate\"\u003e\u003ccode\u003egdb-peda$ searchmem \"/home/naetw/CTF/seccon2016/check/checker\"\nSearching for '/home/naetw/CTF/seccon2016/check/checker' in: None ranges\nFound 3 results, display max 3 items:\n[stack] : 0x7fffffffe1cd (\"/home/naetw/CTF/seccon2016/check/checker\")\n[stack] : 0x7fffffffed7c (\"/home/naetw/CTF/seccon2016/check/checker\")\n[stack] : 0x7fffffffefcf (\"/home/naetw/CTF/seccon2016/check/checker\")\ngdb-peda$ searchmem 0x7fffffffe1cd\nSearching for '0x7fffffffe1cd' in: None ranges\nFound 2 results, display max 2 items:\n libc : 0x7ffff7dd33b8 --\u0026gt; 0x7fffffffe1cd (\"/home/naetw/CTF/seccon2016/check/checker\")\n[stack] : 0x7fffffffde28 --\u0026gt; 0x7fffffffe1cd (\"/home/naetw/CTF/seccon2016/check/checker\")\n\u003c/code\u003e\u003c/pre\u003e\u003c/div\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eBinary Service\u003c/h2\u003e\u003ca id=\"user-content-binary-service\" class=\"anchor\" aria-label=\"Permalink: Binary Service\" href=\"#binary-service\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eNormal:\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003encat -vc ./binary -kl 127.0.0.1 $port\u003c/code\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eWith specific library in two ways:\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003encat -vc 'LD_PRELOAD=/path/to/libc.so ./binary' -kl 127.0.0.1 $port\u003c/code\u003e\u003c/li\u003e\n\u003cli\u003e\u003ccode\u003encat -vc 'LD_LIBRARY_PATH=/path/of/libc.so ./binary' -kl 127.0.0.1 $port\u003c/code\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eAfter this, you can connect to binary service by command \u003ccode\u003enc localhost $port\u003c/code\u003e.\u003c/p\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eFind specific function offset in libc\u003c/h2\u003e\u003ca id=\"user-content-find-specific-function-offset-in-libc\" class=\"anchor\" aria-label=\"Permalink: Find specific function offset in libc\" href=\"#find-specific-function-offset-in-libc\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eIf we leaked libc address of certain function successfully, we could use get libc base address by subtracting the offset of that function.\u003c/p\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eManually\u003c/h3\u003e\u003ca id=\"user-content-manually\" class=\"anchor\" aria-label=\"Permalink: Manually\" href=\"#manually\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003ereadelf -s $libc | grep ${function}@\u003c/code\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eE.g.\u003c/p\u003e\n\u003cdiv class=\"snippet-clipboard-content notranslate position-relative overflow-auto\" data-snippet-clipboard-copy-content=\"$ readelf -s libc-2.19.so | grep system@\n 620: 00040310 56 FUNC GLOBAL DEFAULT 12 __libc_system@@GLIBC_PRIVATE\n 1443: 00040310 56 FUNC WEAK DEFAULT 12 system@@GLIBC_2.0\"\u003e\u003cpre class=\"notranslate\"\u003e\u003ccode\u003e$ readelf -s libc-2.19.so | grep system@\n 620: 00040310 56 FUNC GLOBAL DEFAULT 12 __libc_system@@GLIBC_PRIVATE\n 1443: 00040310 56 FUNC WEAK DEFAULT 12 system@@GLIBC_2.0\n\u003c/code\u003e\u003c/pre\u003e\u003c/div\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eAutomatically\u003c/h3\u003e\u003ca id=\"user-content-automatically\" class=\"anchor\" aria-label=\"Permalink: Automatically\" href=\"#automatically\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eUse \u003ca href=\"https://github.com/Gallopsled/pwntools\"\u003epwntools\u003c/a\u003e, then you can use it in your exploit script.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eE.g.\u003c/p\u003e\n\u003cdiv class=\"highlight highlight-source-python notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"from pwn import *\n\nlibc = ELF('libc.so')\nsystem_off = libc.symbols['system']\"\u003e\u003cpre\u003e\u003cspan class=\"pl-k\"\u003efrom\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003epwn\u003c/span\u003e \u003cspan class=\"pl-k\"\u003eimport\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e\n\n\u003cspan class=\"pl-s1\"\u003elibc\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-en\"\u003eELF\u003c/span\u003e(\u003cspan class=\"pl-s\"\u003e'libc.so'\u003c/span\u003e)\n\u003cspan class=\"pl-s1\"\u003esystem_off\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003elibc\u003c/span\u003e.\u003cspan class=\"pl-c1\"\u003esymbols\u003c/span\u003e[\u003cspan class=\"pl-s\"\u003e'system'\u003c/span\u003e]\u003c/pre\u003e\u003c/div\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eFind '/bin/sh' or 'sh' in library\u003c/h2\u003e\u003ca id=\"user-content-find-binsh-or-sh-in-library\" class=\"anchor\" aria-label=\"Permalink: Find '/bin/sh' or 'sh' in library\" href=\"#find-binsh-or-sh-in-library\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eNeed libc base address first\u003c/p\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eManually\u003c/h3\u003e\u003ca id=\"user-content-manually-1\" class=\"anchor\" aria-label=\"Permalink: Manually\" href=\"#manually-1\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003eobjdump -s libc.so | less\u003c/code\u003e then search 'sh'\u003c/li\u003e\n\u003cli\u003e\u003ccode\u003estrings -tx libc.so | grep /bin/sh\u003c/code\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eAutomatically\u003c/h3\u003e\u003ca id=\"user-content-automatically-1\" class=\"anchor\" aria-label=\"Permalink: Automatically\" href=\"#automatically-1\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eUse \u003ca href=\"https://github.com/Gallopsled/pwntools\"\u003epwntools\u003c/a\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eE.g.\u003c/p\u003e\n\u003cdiv class=\"highlight highlight-source-python notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"from pwn import *\n\nlibc = ELF('libc.so')\n...\nsh = base + next(libc.search('sh\\x00'))\nbinsh = base + next(libc.search('/bin/sh\\x00'))\"\u003e\u003cpre\u003e\u003cspan class=\"pl-k\"\u003efrom\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003epwn\u003c/span\u003e \u003cspan class=\"pl-k\"\u003eimport\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e\n\n\u003cspan class=\"pl-s1\"\u003elibc\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-en\"\u003eELF\u003c/span\u003e(\u003cspan class=\"pl-s\"\u003e'libc.so'\u003c/span\u003e)\n...\n\u003cspan class=\"pl-s1\"\u003esh\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003ebase\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e+\u003c/span\u003e \u003cspan class=\"pl-en\"\u003enext\u003c/span\u003e(\u003cspan class=\"pl-s1\"\u003elibc\u003c/span\u003e.\u003cspan class=\"pl-c1\"\u003esearch\u003c/span\u003e(\u003cspan class=\"pl-s\"\u003e'sh\u003cspan class=\"pl-cce\"\u003e\\x00\u003c/span\u003e'\u003c/span\u003e))\n\u003cspan class=\"pl-s1\"\u003ebinsh\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003ebase\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e+\u003c/span\u003e \u003cspan class=\"pl-en\"\u003enext\u003c/span\u003e(\u003cspan class=\"pl-s1\"\u003elibc\u003c/span\u003e.\u003cspan class=\"pl-c1\"\u003esearch\u003c/span\u003e(\u003cspan class=\"pl-s\"\u003e'/bin/sh\u003cspan class=\"pl-cce\"\u003e\\x00\u003c/span\u003e'\u003c/span\u003e))\u003c/pre\u003e\u003c/div\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eLeak stack address\u003c/h2\u003e\u003ca id=\"user-content-leak-stack-address\" class=\"anchor\" aria-label=\"Permalink: Leak stack address\" href=\"#leak-stack-address\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003e\u003cstrong\u003econstraints\u003c/strong\u003e:\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eHave already leaked libc base address\u003c/li\u003e\n\u003cli\u003eCan leak the content of arbitrary address\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eThere is a symbol \u003ccode\u003eenviron\u003c/code\u003e in libc, whose value is the same as the third argument of \u003ccode\u003emain\u003c/code\u003e function, \u003ccode\u003echar **envp\u003c/code\u003e.\nThe value of \u003ccode\u003echar **envp\u003c/code\u003e is on the stack, thus we can leak stack address with this symbol.\u003c/p\u003e\n\u003cdiv class=\"snippet-clipboard-content notranslate position-relative overflow-auto\" data-snippet-clipboard-copy-content=\"(gdb) list 1\n1 #include \u0026lt;stdlib.h\u0026gt;\n2 #include \u0026lt;stdio.h\u0026gt;\n3\n4 extern char **environ;\n5\n6 int main(int argc, char **argv, char **envp)\n7 {\n8 return 0;\n9 }\n(gdb) x/gx 0x7ffff7a0e000 + 0x3c5f38\n0x7ffff7dd3f38 \u0026lt;environ\u0026gt;: 0x00007fffffffe230\n(gdb) p/x (char **)envp\n$12 = 0x7fffffffe230\"\u003e\u003cpre class=\"notranslate\"\u003e\u003ccode\u003e(gdb) list 1\n1 #include \u0026lt;stdlib.h\u0026gt;\n2 #include \u0026lt;stdio.h\u0026gt;\n3\n4 extern char **environ;\n5\n6 int main(int argc, char **argv, char **envp)\n7 {\n8 return 0;\n9 }\n(gdb) x/gx 0x7ffff7a0e000 + 0x3c5f38\n0x7ffff7dd3f38 \u0026lt;environ\u0026gt;: 0x00007fffffffe230\n(gdb) p/x (char **)envp\n$12 = 0x7fffffffe230\n\u003c/code\u003e\u003c/pre\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003e0x7ffff7a0e000\u003c/code\u003e is current libc base address\u003c/li\u003e\n\u003cli\u003e\u003ccode\u003e0x3c5f38\u003c/code\u003e is offset of \u003ccode\u003eenviron\u003c/code\u003e in libc\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eThis \u003ca href=\"https://www.gnu.org/software/libc/manual/html_node/Program-Arguments.html\" rel=\"nofollow\"\u003emanual\u003c/a\u003e explains details about \u003ccode\u003eenviron\u003c/code\u003e.\u003c/p\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eFork problem in gdb\u003c/h2\u003e\u003ca id=\"user-content-fork-problem-in-gdb\" class=\"anchor\" aria-label=\"Permalink: Fork problem in gdb\" href=\"#fork-problem-in-gdb\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eWhen you use \u003cstrong\u003egdb\u003c/strong\u003e to debug a binary with \u003ccode\u003efork()\u003c/code\u003e function, you can use the following command to determine which process to follow (The default setting of original gdb is parent, while that of gdb-peda is child.):\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003eset follow-fork-mode parent\u003c/code\u003e\u003c/li\u003e\n\u003cli\u003e\u003ccode\u003eset follow-fork-mode child\u003c/code\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eAlternatively, using \u003ccode\u003eset detach-on-fork off\u003c/code\u003e, we can then control both sides of each fork. Using \u003ccode\u003einferior X\u003c/code\u003e where \u003ccode\u003eX\u003c/code\u003e is any of the numbers that show up for \u003ccode\u003einfo inferiors\u003c/code\u003e will switch to that side of the fork. This is useful if both sides of the fork are necessary to attack a challenge, and the simple \u003ccode\u003efollow\u003c/code\u003e ones above aren't sufficient.\u003c/p\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eSecret of a mysterious section - .tls\u003c/h2\u003e\u003ca id=\"user-content-secret-of-a-mysterious-section---tls\" class=\"anchor\" aria-label=\"Permalink: Secret of a mysterious section - .tls\" href=\"#secret-of-a-mysterious-section---tls\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003e\u003cstrong\u003econstraints\u003c/strong\u003e:\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eNeed \u003ccode\u003emalloc\u003c/code\u003e function and you can malloc with arbitrary size\u003c/li\u003e\n\u003cli\u003eArbitrary address leaking\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eWe make \u003ccode\u003emalloc\u003c/code\u003e use \u003ccode\u003emmap\u003c/code\u003e to allocate memory(size 0x21000 is enough). In general, these pages will be placed at the address just before \u003ccode\u003e.tls\u003c/code\u003e section.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003eThere is some useful information on \u003cstrong\u003e\u003ccode\u003e.tls\u003c/code\u003e\u003c/strong\u003e, such as the address of \u003ccode\u003emain_arena\u003c/code\u003e, \u003ccode\u003ecanary\u003c/code\u003e (value of stack guard), and a strange \u003ccode\u003estack address\u003c/code\u003e which points to somewhere on the stack but with a fixed offset.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003e\u003cstrong\u003eBefore calling mmap:\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv class=\"snippet-clipboard-content notranslate position-relative overflow-auto\" data-snippet-clipboard-copy-content=\"7fecbfe4d000-7fecbfe51000 r--p 001bd000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so\n7fecbfe51000-7fecbfe53000 rw-p 001c1000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so\n7fecbfe53000-7fecbfe57000 rw-p 00000000 00:00 0\n7fecbfe57000-7fecbfe7c000 r-xp 00000000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\n7fecc0068000-7fecc006a000 rw-p 00000000 00:00 0 \u0026lt;- .tls section\n7fecc0078000-7fecc007b000 rw-p 00000000 00:00 0\n7fecc007b000-7fecc007c000 r--p 00024000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\n7fecc007c000-7fecc007d000 rw-p 00025000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\"\u003e\u003cpre class=\"notranslate\"\u003e\u003ccode\u003e7fecbfe4d000-7fecbfe51000 r--p 001bd000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so\n7fecbfe51000-7fecbfe53000 rw-p 001c1000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so\n7fecbfe53000-7fecbfe57000 rw-p 00000000 00:00 0\n7fecbfe57000-7fecbfe7c000 r-xp 00000000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\n7fecc0068000-7fecc006a000 rw-p 00000000 00:00 0 \u0026lt;- .tls section\n7fecc0078000-7fecc007b000 rw-p 00000000 00:00 0\n7fecc007b000-7fecc007c000 r--p 00024000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\n7fecc007c000-7fecc007d000 rw-p 00025000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\n\u003c/code\u003e\u003c/pre\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003e\u003cstrong\u003eAfter call mmap:\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv class=\"snippet-clipboard-content notranslate position-relative overflow-auto\" data-snippet-clipboard-copy-content=\"7fecbfe4d000-7fecbfe51000 r--p 001bd000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so\n7fecbfe51000-7fecbfe53000 rw-p 001c1000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so\n7fecbfe53000-7fecbfe57000 rw-p 00000000 00:00 0\n7fecbfe57000-7fecbfe7c000 r-xp 00000000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\n7fecc0045000-7fecc006a000 rw-p 00000000 00:00 0 \u0026lt;- memory of mmap + .tls section\n7fecc0078000-7fecc007b000 rw-p 00000000 00:00 0\n7fecc007b000-7fecc007c000 r--p 00024000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\n7fecc007c000-7fecc007d000 rw-p 00025000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\"\u003e\u003cpre class=\"notranslate\"\u003e\u003ccode\u003e7fecbfe4d000-7fecbfe51000 r--p 001bd000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so\n7fecbfe51000-7fecbfe53000 rw-p 001c1000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so\n7fecbfe53000-7fecbfe57000 rw-p 00000000 00:00 0\n7fecbfe57000-7fecbfe7c000 r-xp 00000000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\n7fecc0045000-7fecc006a000 rw-p 00000000 00:00 0 \u0026lt;- memory of mmap + .tls section\n7fecc0078000-7fecc007b000 rw-p 00000000 00:00 0\n7fecc007b000-7fecc007c000 r--p 00024000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\n7fecc007c000-7fecc007d000 rw-p 00025000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so\n\u003c/code\u003e\u003c/pre\u003e\u003c/div\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003ePredictable RNG(Random Number Generator)\u003c/h2\u003e\u003ca id=\"user-content-predictable-rngrandom-number-generator\" class=\"anchor\" aria-label=\"Permalink: Predictable RNG(Random Number Generator)\" href=\"#predictable-rngrandom-number-generator\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eWhen the binary uses the RNG to make the address of important information or sth, we can guess the same value if it's predictable.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003eAssuming that it's predictable, we can use \u003ca href=\"https://docs.python.org/2/library/ctypes.html\" rel=\"nofollow\"\u003ectypes\u003c/a\u003e which is a build-in module in Python.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003e\u003cstrong\u003ectypes\u003c/strong\u003e allows calling a function in DLL(Dynamic-Link Library) or Shared Library.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003eTherefore, if binary has an init_proc like this:\u003c/p\u003e\n\u003cdiv class=\"highlight highlight-source-c notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"srand(time(NULL));\nwhile(addr \u0026lt;= 0x10000){\n addr = rand() \u0026amp; 0xfffff000;\n}\nsecret = mmap(addr,0x1000,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANONYMOUS ,-1,0);\nif(secret == -1){\n puts(\u0026quot;mmap error\u0026quot;);\n exit(0);\n}\"\u003e\u003cpre\u003e\u003cspan class=\"pl-en\"\u003esrand\u003c/span\u003e(\u003cspan class=\"pl-en\"\u003etime\u003c/span\u003e(\u003cspan class=\"pl-c1\"\u003eNULL\u003c/span\u003e));\n\u003cspan class=\"pl-k\"\u003ewhile\u003c/span\u003e(\u003cspan class=\"pl-s1\"\u003eaddr\u003c/span\u003e \u0026lt;= \u003cspan class=\"pl-c1\"\u003e0x10000\u003c/span\u003e){\n \u003cspan class=\"pl-s1\"\u003eaddr\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-en\"\u003erand\u003c/span\u003e() \u003cspan class=\"pl-c1\"\u003e\u0026amp;\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e0xfffff000\u003c/span\u003e;\n}\n\u003cspan class=\"pl-s1\"\u003esecret\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-en\"\u003emmap\u003c/span\u003e(\u003cspan class=\"pl-s1\"\u003eaddr\u003c/span\u003e,\u003cspan class=\"pl-c1\"\u003e0x1000\u003c/span\u003e,\u003cspan class=\"pl-c1\"\u003ePROT_READ\u003c/span\u003e|\u003cspan class=\"pl-c1\"\u003ePROT_WRITE\u003c/span\u003e,\u003cspan class=\"pl-c1\"\u003eMAP_PRIVATE\u003c/span\u003e|\u003cspan class=\"pl-c1\"\u003eMAP_ANONYMOUS\u003c/span\u003e ,\u003cspan class=\"pl-c1\"\u003e-1\u003c/span\u003e,\u003cspan class=\"pl-c1\"\u003e0\u003c/span\u003e);\n\u003cspan class=\"pl-k\"\u003eif\u003c/span\u003e(\u003cspan class=\"pl-s1\"\u003esecret\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e==\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e-1\u003c/span\u003e){\n \u003cspan class=\"pl-en\"\u003eputs\u003c/span\u003e(\u003cspan class=\"pl-s\"\u003e\"mmap error\"\u003c/span\u003e);\n \u003cspan class=\"pl-en\"\u003eexit\u003c/span\u003e(\u003cspan class=\"pl-c1\"\u003e0\u003c/span\u003e);\n}\u003c/pre\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eThen we can use \u003cstrong\u003ectypes\u003c/strong\u003e to get the same value of addr.\u003c/p\u003e\n\u003cdiv class=\"highlight highlight-source-python notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"import ctypes\nLIBC = ctypes.cdll.LoadLibrary('/path/to/dll')\nLIBC.srand(LIBC.time(0))\naddr = LIBC.rand() \u0026amp; 0xfffff000\"\u003e\u003cpre\u003e\u003cspan class=\"pl-k\"\u003eimport\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003ectypes\u003c/span\u003e\n\u003cspan class=\"pl-c1\"\u003eLIBC\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003ectypes\u003c/span\u003e.\u003cspan class=\"pl-c1\"\u003ecdll\u003c/span\u003e.\u003cspan class=\"pl-c1\"\u003eLoadLibrary\u003c/span\u003e(\u003cspan class=\"pl-s\"\u003e'/path/to/dll'\u003c/span\u003e)\n\u003cspan class=\"pl-c1\"\u003eLIBC\u003c/span\u003e.\u003cspan class=\"pl-c1\"\u003esrand\u003c/span\u003e(\u003cspan class=\"pl-c1\"\u003eLIBC\u003c/span\u003e.\u003cspan class=\"pl-c1\"\u003etime\u003c/span\u003e(\u003cspan class=\"pl-c1\"\u003e0\u003c/span\u003e))\n\u003cspan class=\"pl-s1\"\u003eaddr\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003eLIBC\u003c/span\u003e.\u003cspan class=\"pl-c1\"\u003erand\u003c/span\u003e() \u003cspan class=\"pl-c1\"\u003e\u0026amp;\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e0xfffff000\u003c/span\u003e\u003c/pre\u003e\u003c/div\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eMake stack executable\u003c/h2\u003e\u003ca id=\"user-content-make-stack-executable\" class=\"anchor\" aria-label=\"Permalink: Make stack executable\" href=\"#make-stack-executable\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ca href=\"http://radare.today/posts/defeating-baby_rop-with-radare2/\" rel=\"nofollow\"\u003elink1\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"https://sploitfun.wordpress.com/author/sploitfun/\" rel=\"nofollow\"\u003elink2\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003eHaven't read yet orz\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eUse one-gadget-RCE instead of system\u003c/h2\u003e\u003ca id=\"user-content-use-one-gadget-rce-instead-of-system\" class=\"anchor\" aria-label=\"Permalink: Use one-gadget-RCE instead of system\" href=\"#use-one-gadget-rce-instead-of-system\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003e\u003cstrong\u003econstraints\u003c/strong\u003e:\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eHave libc base address\u003c/li\u003e\n\u003cli\u003eWrite to arbitrary address\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eAlmost every pwnable challenge needs to call \u003ccode\u003esystem('/bin/sh')\u003c/code\u003e in the end of the exploit, but if we want to call that, we have to manipulate the parameters and, of course, hijack some functions to \u003ccode\u003esystem\u003c/code\u003e. What if we \u003cstrong\u003ecan't\u003c/strong\u003e manipulate the parameter?\u003c/p\u003e\n\u003cp dir=\"auto\"\u003eUse \u003ca href=\"http://j00ru.vexillium.org/blog/24_03_15/dragons_ctf.pdf\" rel=\"nofollow\"\u003eone-gadget-RCE\u003c/a\u003e!\u003c/p\u003e\n\u003cp dir=\"auto\"\u003eWith \u003cstrong\u003eone-gadget-RCE\u003c/strong\u003e, we can just hijack \u003ccode\u003e.got.plt\u003c/code\u003e or something we can use to control eip to make program jump to \u003cstrong\u003eone-gadget\u003c/strong\u003e, but there are some constraints that need satisfying before using it.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003eThere are lots of \u003cstrong\u003eone-gadgets\u003c/strong\u003e in libc. Each one has different constraints but those are similar. Each constraint is about the state of registers.\u003c/p\u003e\n\u003cp dir=\"auto\"\u003eE.g.\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eebx is the address of \u003ccode\u003erw-p\u003c/code\u003e area of libc\u003c/li\u003e\n\u003cli\u003e[esp+0x34] == NULL\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eHow can we get these constraints? Here is an useful tool \u003ca href=\"https://github.com/david942j/one_gadget\"\u003eone_gadget\u003c/a\u003e !!!!\u003c/p\u003e\n\u003cp dir=\"auto\"\u003eSo if we can satisfy those constraints, we can get the shell more easily.\u003c/p\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eHijack hook function\u003c/h2\u003e\u003ca id=\"user-content-hijack-hook-function\" class=\"anchor\" aria-label=\"Permalink: Hijack hook function\" href=\"#hijack-hook-function\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003e\u003cstrong\u003econstraints\u003c/strong\u003e:\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eHave libc base address\u003c/li\u003e\n\u003cli\u003eWrite to arbitrary address\u003c/li\u003e\n\u003cli\u003eThe program uses \u003ccode\u003emalloc\u003c/code\u003e, \u003ccode\u003efree\u003c/code\u003e or \u003ccode\u003erealloc\u003c/code\u003e.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eBy manual:\u003c/p\u003e\n\u003cblockquote\u003e\n\u003cp dir=\"auto\"\u003eThe GNU C Library lets you modify the behavior of \u003ccode\u003emalloc\u003c/code\u003e, \u003ccode\u003erealloc\u003c/code\u003e, and \u003ccode\u003efree\u003c/code\u003e by specifying appropriate hook functions. You can use these hooks to help you debug programs that use dynamic memory allocation, for example.\u003c/p\u003e\n\u003c/blockquote\u003e\n\u003cp dir=\"auto\"\u003eThere are hook variables declared in malloc.h and their default values are \u003ccode\u003e0x0\u003c/code\u003e.\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003e__malloc_hook\u003c/code\u003e\u003c/li\u003e\n\u003cli\u003e\u003ccode\u003e__free_hook\u003c/code\u003e\u003c/li\u003e\n\u003cli\u003e...\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp dir=\"auto\"\u003eSince they are used to help us debug programs, they are writable during the execution.\u003c/p\u003e\n\u003cdiv class=\"snippet-clipboard-content notranslate position-relative overflow-auto\" data-snippet-clipboard-copy-content=\"0xf77228e0 \u0026lt;__free_hook\u0026gt;: 0x00000000\n0xf7722000 0xf7727000 rw-p mapped\"\u003e\u003cpre class=\"notranslate\"\u003e\u003ccode\u003e0xf77228e0 \u0026lt;__free_hook\u0026gt;: 0x00000000\n0xf7722000 0xf7727000 rw-p mapped\n\u003c/code\u003e\u003c/pre\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eLet's look into the \u003ca href=\"https://code.woboq.org/userspace/glibc/malloc/malloc.c.html#2917\" rel=\"nofollow\"\u003esrc\u003c/a\u003e of malloc.c. I will use \u003ccode\u003e__libc_free\u003c/code\u003e to demo.\u003c/p\u003e\n\u003cdiv class=\"highlight highlight-source-c notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"void (*hook) (void *, const void *) = atomic_forced_read (__free_hook);\nif (__builtin_expect (hook != NULL, 0))\n{\n (*hook)(mem, RETURN_ADDRESS (0));\n return;\n}\"\u003e\u003cpre\u003e\u003cspan class=\"pl-smi\"\u003evoid\u003c/span\u003e (\u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e\u003cspan class=\"pl-s1\"\u003ehook\u003c/span\u003e) (\u003cspan class=\"pl-smi\"\u003evoid\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e, \u003cspan class=\"pl-k\"\u003econst\u003c/span\u003e \u003cspan class=\"pl-smi\"\u003evoid\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e) \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-en\"\u003eatomic_forced_read\u003c/span\u003e (\u003cspan class=\"pl-s1\"\u003e__free_hook\u003c/span\u003e);\n\u003cspan class=\"pl-k\"\u003eif\u003c/span\u003e (\u003cspan class=\"pl-en\"\u003e__builtin_expect\u003c/span\u003e (\u003cspan class=\"pl-s1\"\u003ehook\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e!=\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003eNULL\u003c/span\u003e, \u003cspan class=\"pl-c1\"\u003e0\u003c/span\u003e))\n{\n (\u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e\u003cspan class=\"pl-s1\"\u003ehook\u003c/span\u003e)(\u003cspan class=\"pl-s1\"\u003emem\u003c/span\u003e, \u003cspan class=\"pl-en\"\u003eRETURN_ADDRESS\u003c/span\u003e (\u003cspan class=\"pl-c1\"\u003e0\u003c/span\u003e));\n \u003cspan class=\"pl-k\"\u003ereturn\u003c/span\u003e;\n}\u003c/pre\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eIt checks the value of \u003ccode\u003e__free_hook\u003c/code\u003e. If it's not NULL, it will call the hook function first. Here, we would like to use \u003cstrong\u003eone-gadget-RCE\u003c/strong\u003e. Since hook function is called in the libc, the constraints of \u003cstrong\u003eone-gadget\u003c/strong\u003e are usually satisfied.\u003c/p\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eUse printf to trigger malloc and free\u003c/h2\u003e\u003ca id=\"user-content-use-printf-to-trigger-malloc-and-free\" class=\"anchor\" aria-label=\"Permalink: Use printf to trigger malloc and free\" href=\"#use-printf-to-trigger-malloc-and-free\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eLook into the source of printf, there are several places which may trigger malloc. Take \u003ca href=\"https://code.woboq.org/userspace/glibc/stdio-common/vfprintf.c.html#1470\" rel=\"nofollow\"\u003evfprintf.c line 1470\u003c/a\u003e for example:\u003c/p\u003e\n\u003cdiv class=\"highlight highlight-source-c notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"#define EXTSIZ 32\nenum { WORK_BUFFER_SIZE = 1000 };\n\nif (width \u0026gt;= WORK_BUFFER_SIZE - EXTSIZ)\n{\n /* We have to use a special buffer. */\n size_t needed = ((size_t) width + EXTSIZ) * sizeof (CHAR_T);\n if (__libc_use_alloca (needed))\n workend = (CHAR_T *) alloca (needed) + width + EXTSIZ;\n else\n {\n workstart = (CHAR_T *) malloc (needed);\n if (workstart == NULL)\n {\n done = -1;\n goto all_done;\n }\n workend = workstart + width + EXTSIZ;\n }\n}\"\u003e\u003cpre\u003e\u003cspan class=\"pl-k\"\u003e#define\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003eEXTSIZ\u003c/span\u003e 32\n\u003cspan class=\"pl-k\"\u003eenum\u003c/span\u003e { \u003cspan class=\"pl-c1\"\u003eWORK_BUFFER_SIZE\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e1000\u003c/span\u003e };\n\n\u003cspan class=\"pl-k\"\u003eif\u003c/span\u003e (\u003cspan class=\"pl-s1\"\u003ewidth\u003c/span\u003e \u0026gt;= \u003cspan class=\"pl-c1\"\u003eWORK_BUFFER_SIZE\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e-\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003eEXTSIZ\u003c/span\u003e)\n{\n \u003cspan class=\"pl-c\"\u003e/* We have to use a special buffer. */\u003c/span\u003e\n \u003cspan class=\"pl-smi\"\u003esize_t\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003eneeded\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e ((\u003cspan class=\"pl-smi\"\u003esize_t\u003c/span\u003e) \u003cspan class=\"pl-s1\"\u003ewidth\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e+\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003eEXTSIZ\u003c/span\u003e) \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e \u003cspan class=\"pl-k\"\u003esizeof\u003c/span\u003e (\u003cspan class=\"pl-c1\"\u003eCHAR_T\u003c/span\u003e);\n \u003cspan class=\"pl-k\"\u003eif\u003c/span\u003e (\u003cspan class=\"pl-en\"\u003e__libc_use_alloca\u003c/span\u003e (\u003cspan class=\"pl-s1\"\u003eneeded\u003c/span\u003e))\n \u003cspan class=\"pl-s1\"\u003eworkend\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e (\u003cspan class=\"pl-smi\"\u003eCHAR_T\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e) \u003cspan class=\"pl-en\"\u003ealloca\u003c/span\u003e (\u003cspan class=\"pl-s1\"\u003eneeded\u003c/span\u003e) \u003cspan class=\"pl-c1\"\u003e+\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003ewidth\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e+\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003eEXTSIZ\u003c/span\u003e;\n \u003cspan class=\"pl-k\"\u003eelse\u003c/span\u003e\n {\n \u003cspan class=\"pl-s1\"\u003eworkstart\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e (\u003cspan class=\"pl-smi\"\u003eCHAR_T\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e) \u003cspan class=\"pl-en\"\u003emalloc\u003c/span\u003e (\u003cspan class=\"pl-s1\"\u003eneeded\u003c/span\u003e);\n \u003cspan class=\"pl-k\"\u003eif\u003c/span\u003e (\u003cspan class=\"pl-s1\"\u003eworkstart\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e==\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003eNULL\u003c/span\u003e)\n {\n \u003cspan class=\"pl-s1\"\u003edone\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e-1\u003c/span\u003e;\n goto \u003cspan class=\"pl-ent\"\u003eall_done\u003c/span\u003e;\n }\n \u003cspan class=\"pl-s1\"\u003eworkend\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e=\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003eworkstart\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e+\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003ewidth\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e+\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003eEXTSIZ\u003c/span\u003e;\n }\n}\u003c/pre\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eWe can find that \u003ccode\u003emalloc\u003c/code\u003e will be triggered if the width field is large enough.(Of course, \u003ccode\u003efree\u003c/code\u003e will also be triggered at the end of printf if \u003ccode\u003emalloc\u003c/code\u003e has been triggered.) However, WORK_BUFFER_SIZE is not large enough, since we need to go to \u003cstrong\u003eelse\u003c/strong\u003e block. Let's take a look at \u003ccode\u003e__libc_use_alloca\u003c/code\u003e and see what exactly the minimum size of width we should give.\u003c/p\u003e\n\u003cdiv class=\"highlight highlight-source-c notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"\n/* Minimum size for a thread. We are free to choose a reasonable value. */\n#define PTHREAD_STACK_MIN 16384\n\n#define __MAX_ALLOCA_CUTOFF 65536\n\nint __libc_use_alloca (size_t size)\n{\n return (__builtin_expect (size \u0026lt;= PTHREAD_STACK_MIN / 4, 1)\n || __builtin_expect (__libc_alloca_cutoff (size), 1));\n}\n\nint __libc_alloca_cutoff (size_t size)\n{\n\treturn size \u0026lt;= (MIN (__MAX_ALLOCA_CUTOFF,\n\t\t\t\t\tTHREAD_GETMEM (THREAD_SELF, stackblock_size) / 4\n\t\t\t\t\t/* The main thread, before the thread library is\n\t\t\t\t\t\tinitialized, has zero in the stackblock_size\n\t\t\t\t\t\telement. Since it is the main thread we can\n\t\t\t\t\t\tassume the maximum available stack space. */\n\t\t\t\t\t?: __MAX_ALLOCA_CUTOFF * 4));\n}\"\u003e\u003cpre\u003e\u003cspan class=\"pl-c\"\u003e/* Minimum size for a thread. We are free to choose a reasonable value. */\u003c/span\u003e\n\u003cspan class=\"pl-k\"\u003e#define\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003ePTHREAD_STACK_MIN\u003c/span\u003e 16384\n\n\u003cspan class=\"pl-k\"\u003e#define\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003e__MAX_ALLOCA_CUTOFF\u003c/span\u003e 65536\n\n\u003cspan class=\"pl-smi\"\u003eint\u003c/span\u003e \u003cspan class=\"pl-en\"\u003e__libc_use_alloca\u003c/span\u003e (\u003cspan class=\"pl-smi\"\u003esize_t\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003esize\u003c/span\u003e)\n{\n \u003cspan class=\"pl-k\"\u003ereturn\u003c/span\u003e (\u003cspan class=\"pl-en\"\u003e__builtin_expect\u003c/span\u003e (\u003cspan class=\"pl-s1\"\u003esize\u003c/span\u003e \u0026lt;= \u003cspan class=\"pl-c1\"\u003ePTHREAD_STACK_MIN\u003c/span\u003e / \u003cspan class=\"pl-c1\"\u003e4\u003c/span\u003e, \u003cspan class=\"pl-c1\"\u003e1\u003c/span\u003e)\n \u003cspan class=\"pl-c1\"\u003e||\u003c/span\u003e \u003cspan class=\"pl-en\"\u003e__builtin_expect\u003c/span\u003e (\u003cspan class=\"pl-en\"\u003e__libc_alloca_cutoff\u003c/span\u003e (\u003cspan class=\"pl-s1\"\u003esize\u003c/span\u003e), \u003cspan class=\"pl-c1\"\u003e1\u003c/span\u003e));\n}\n\n\u003cspan class=\"pl-smi\"\u003eint\u003c/span\u003e \u003cspan class=\"pl-en\"\u003e__libc_alloca_cutoff\u003c/span\u003e (\u003cspan class=\"pl-smi\"\u003esize_t\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003esize\u003c/span\u003e)\n{\n\t\u003cspan class=\"pl-k\"\u003ereturn\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003esize\u003c/span\u003e \u0026lt;= (\u003cspan class=\"pl-en\"\u003eMIN\u003c/span\u003e (\u003cspan class=\"pl-s1\"\u003e__MAX_ALLOCA_CUTOFF\u003c/span\u003e,\n\t\t\t\t\t\u003cspan class=\"pl-en\"\u003eTHREAD_GETMEM\u003c/span\u003e (\u003cspan class=\"pl-c1\"\u003eTHREAD_SELF\u003c/span\u003e, \u003cspan class=\"pl-s1\"\u003estackblock_size\u003c/span\u003e) / \u003cspan class=\"pl-c1\"\u003e4\u003c/span\u003e\n\t\t\t\t\t\u003cspan class=\"pl-c\"\u003e/* The main thread, before the thread library is\u003c/span\u003e\n\u003cspan class=\"pl-c\"\u003e\t\t\t\t\t\tinitialized, has zero in the stackblock_size\u003c/span\u003e\n\u003cspan class=\"pl-c\"\u003e\t\t\t\t\t\telement. Since it is the main thread we can\u003c/span\u003e\n\u003cspan class=\"pl-c\"\u003e\t\t\t\t\t\tassume the maximum available stack space. */\u003c/span\u003e\n\t\t\t\t\t?: \u003cspan class=\"pl-s1\"\u003e__MAX_ALLOCA_CUTOFF\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e4\u003c/span\u003e));\n}\u003c/pre\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eWe have to make sure that:\u003c/p\u003e\n\u003col dir=\"auto\"\u003e\n\u003cli\u003e\u003ccode\u003esize \u0026gt; PTHREAD_STACK_MIN / 4\u003c/code\u003e\u003c/li\u003e\n\u003cli\u003e\u003ccode\u003esize \u0026gt; MIN(__MAX_ALLOCA_CUTOFF, THREAD_GETMEM(THREAD_SELF, stackblock_size) / 4 ?: __MAX_ALLOCA_CUTOFF * 4)\u003c/code\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eI did not fully understand what exactly the function - THREAD_GETMEM do, but it seems that it mostly returns 0.\u003c/li\u003e\n\u003cli\u003eTherefore, the second condition is usually \u003ccode\u003esize \u0026gt; 65536\u003c/code\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp dir=\"auto\"\u003eMore details:\u003c/p\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003e\u003ca href=\"https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html\" rel=\"nofollow\"\u003e__builtin_expect\u003c/a\u003e\u003c/li\u003e\n\u003cli\u003e\u003ca href=\"https://code.woboq.org/userspace/glibc/sysdeps/x86_64/nptl/tls.h.html#_M/THREAD_GETMEM\" rel=\"nofollow\"\u003eTHREAD_GETMEM\u003c/a\u003e\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch3 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003econclusion\u003c/h3\u003e\u003ca id=\"user-content-conclusion\" class=\"anchor\" aria-label=\"Permalink: conclusion\" href=\"#conclusion\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cul dir=\"auto\"\u003e\n\u003cli\u003eThe minimum size of width to trigger \u003ccode\u003emalloc\u003c/code\u003e \u0026amp; \u003ccode\u003efree\u003c/code\u003e is 65537 most of the time.\u003c/li\u003e\n\u003cli\u003eIf there is a Format String Vulnerability and the program ends right after calling \u003ccode\u003eprintf(buf)\u003c/code\u003e, we can hijack \u003ccode\u003e__malloc_hook\u003c/code\u003e or \u003ccode\u003e__free_hook\u003c/code\u003e with \u003ccode\u003eone-gadget\u003c/code\u003e and use the trick mentioned above to trigger \u003ccode\u003emalloc\u003c/code\u003e \u0026amp; \u003ccode\u003efree\u003c/code\u003e then we can still get the shell even there is no more function call or sth after \u003ccode\u003eprintf(buf)\u003c/code\u003e.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cdiv class=\"markdown-heading\" dir=\"auto\"\u003e\u003ch2 tabindex=\"-1\" class=\"heading-element\" dir=\"auto\"\u003eUse execveat to open a shell\u003c/h2\u003e\u003ca id=\"user-content-use-execveat-to-open-a-shell\" class=\"anchor\" aria-label=\"Permalink: Use execveat to open a shell\" href=\"#use-execveat-to-open-a-shell\"\u003e\u003csvg class=\"octicon octicon-link\" viewBox=\"0 0 16 16\" version=\"1.1\" width=\"16\" height=\"16\" aria-hidden=\"true\"\u003e\u003cpath d=\"m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z\"\u003e\u003c/path\u003e\u003c/svg\u003e\u003c/a\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eWhen it comes to opening a shell with system call, \u003ccode\u003eexecve\u003c/code\u003e always pops up in mind. However, it's not always easily available due to the lack of gadgets or others constraints.\u003cbr\u003e\nActually, there is a system call, \u003ccode\u003eexecveat\u003c/code\u003e, with following prototype:\u003c/p\u003e\n\u003cdiv class=\"highlight highlight-source-c notranslate position-relative overflow-auto\" dir=\"auto\" data-snippet-clipboard-copy-content=\"int execveat(int dirfd, const char *pathname,\n char *const argv[], char *const envp[],\n int flags);\"\u003e\u003cpre\u003e\u003cspan class=\"pl-smi\"\u003eint\u003c/span\u003e \u003cspan class=\"pl-en\"\u003eexecveat\u003c/span\u003e(\u003cspan class=\"pl-smi\"\u003eint\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003edirfd\u003c/span\u003e, \u003cspan class=\"pl-k\"\u003econst\u003c/span\u003e \u003cspan class=\"pl-smi\"\u003echar\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e\u003cspan class=\"pl-s1\"\u003epathname\u003c/span\u003e,\n \u003cspan class=\"pl-smi\"\u003echar\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e\u003cspan class=\"pl-k\"\u003econst\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003eargv\u003c/span\u003e[], \u003cspan class=\"pl-smi\"\u003echar\u003c/span\u003e \u003cspan class=\"pl-c1\"\u003e*\u003c/span\u003e\u003cspan class=\"pl-k\"\u003econst\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003eenvp\u003c/span\u003e[],\n \u003cspan class=\"pl-smi\"\u003eint\u003c/span\u003e \u003cspan class=\"pl-s1\"\u003eflags\u003c/span\u003e);\u003c/pre\u003e\u003c/div\u003e\n\u003cp dir=\"auto\"\u003eAccording to its \u003ca href=\"http://man7.org/linux/man-pages/man2/execveat.2.html\" rel=\"nofollow\"\u003eman page\u003c/a\u003e, it operates in the same way as \u003ccode\u003eexecve\u003c/code\u003e. As for the additional arguments, it mentions that:\u003c/p\u003e\n\u003cblockquote\u003e\n\u003cp dir=\"auto\"\u003eIf pathname is absolute, then dirfd is ignored.\u003c/p\u003e\n\u003c/blockquote\u003e\n\u003cp dir=\"auto\"\u003eHence, if we make \u003ccode\u003epathname\u003c/code\u003e point to \u003ccode\u003e\"/bin/sh\"\u003c/code\u003e, and set \u003ccode\u003eargv\u003c/code\u003e, \u003ccode\u003eenvp\u003c/code\u003e and \u003ccode\u003eflags\u003c/code\u003e to 0, we can still get a shell whatever the value of \u003ccode\u003edirfd\u003c/code\u003e.\u003c/p\u003e\n\u003c/article\u003e","loaded":true,"timedOut":false,"errorMessage":null,"headerInfo":{"toc":[{"level":1,"text":"CTF-pwn-tips","anchor":"ctf-pwn-tips","htmlText":"CTF-pwn-tips"},{"level":1,"text":"Catalog","anchor":"catalog","htmlText":"Catalog"},{"level":2,"text":"Overflow","anchor":"overflow","htmlText":"Overflow"},{"level":3,"text":"scanf","anchor":"scanf","htmlText":"scanf"},{"level":3,"text":"gets","anchor":"gets","htmlText":"gets"},{"level":3,"text":"read","anchor":"read","htmlText":"read"},{"level":3,"text":"strcpy","anchor":"strcpy","htmlText":"strcpy"},{"level":3,"text":"strcat","anchor":"strcat","htmlText":"strcat"},{"level":2,"text":"Find string in gdb","anchor":"find-string-in-gdb","htmlText":"Find string in gdb"},{"level":3,"text":"gdb","anchor":"gdb","htmlText":"gdb"},{"level":3,"text":"gdb peda","anchor":"gdb-peda","htmlText":"gdb peda"},{"level":2,"text":"Binary Service","anchor":"binary-service","htmlText":"Binary Service"},{"level":2,"text":"Find specific function offset in libc","anchor":"find-specific-function-offset-in-libc","htmlText":"Find specific function offset in libc"},{"level":3,"text":"Manually","anchor":"manually","htmlText":"Manually"},{"level":3,"text":"Automatically","anchor":"automatically","htmlText":"Automatically"},{"level":2,"text":"Find '/bin/sh' or 'sh' in library","anchor":"find-binsh-or-sh-in-library","htmlText":"Find '/bin/sh' or 'sh' in library"},{"level":3,"text":"Manually","anchor":"manually-1","htmlText":"Manually"},{"level":3,"text":"Automatically","anchor":"automatically-1","htmlText":"Automatically"},{"level":2,"text":"Leak stack address","anchor":"leak-stack-address","htmlText":"Leak stack address"},{"level":2,"text":"Fork problem in gdb","anchor":"fork-problem-in-gdb","htmlText":"Fork problem in gdb"},{"level":2,"text":"Secret of a mysterious section - .tls","anchor":"secret-of-a-mysterious-section---tls","htmlText":"Secret of a mysterious section - 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QkQOb js-snippet-clipboard-copy-unpositioned undefined" data-hpc="true"><article class="markdown-body entry-content container-lg" itemprop="text"><div class="markdown-heading" dir="auto"><h1 tabindex="-1" class="heading-element" dir="auto">CTF-pwn-tips</h1><a id="user-content-ctf-pwn-tips" class="anchor" aria-label="Permalink: CTF-pwn-tips" href="#ctf-pwn-tips"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <div class="markdown-heading" dir="auto"><h1 tabindex="-1" class="heading-element" dir="auto">Catalog</h1><a id="user-content-catalog" class="anchor" aria-label="Permalink: Catalog" href="#catalog"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li><a href="#overflow">Overflow</a></li> <li><a href="#find-string-in-gdb">Find string in gdb</a></li> <li><a href="#binary-service">Binary Service</a></li> <li><a href="#find-specific-function-offset-in-libc">Find specific function offset in libc</a></li> <li><a href="#find-binsh-or-sh-in-library">Find '/bin/sh' or 'sh' in library</a></li> <li><a href="#leak-stack-address">Leak stack address</a></li> <li><a href="#fork-problem-in-gdb">Fork problem in gdb</a></li> <li><a href="#secret-of-a-mysterious-section---tls">Secret of a mysterious section - .tls</a></li> <li><a href="#predictable-rngrandom-number-generator">Predictable RNG(Random Number Generator)</a></li> <li><a href="#make-stack-executable">Make stack executable</a></li> <li><a href="#use-one-gadget-rce-instead-of-system">Use one-gadget-RCE instead of system</a></li> <li><a href="#hijack-hook-function">Hijack hook function</a></li> <li><a href="#use-printf-to-trigger-malloc-and-free">Use printf to trigger malloc and free</a></li> <li><a href="#use-execveat-to-open-a-shell">Use execveat to open a shell</a></li> </ul> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Overflow</h2><a id="user-content-overflow" class="anchor" aria-label="Permalink: Overflow" href="#overflow"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">Assume that: <code>char buf[40]</code> and <code>signed int num</code></p> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">scanf</h3><a id="user-content-scanf" class="anchor" aria-label="Permalink: scanf" href="#scanf"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li> <p dir="auto"><code>scanf("%s", buf)</code></p> <ul dir="auto"> <li><code>%s</code> doesn't have boundary check.</li> <li><strong>pwnable</strong></li> </ul> </li> <li> <p dir="auto"><code>scanf("%39s", buf)</code></p> <ul dir="auto"> <li><code>%39s</code> only takes 39 bytes from the input and puts NULL byte at the end of input.</li> <li><strong>useless</strong></li> </ul> </li> <li> <p dir="auto"><code>scanf("%40s", buf)</code></p> <ul dir="auto"> <li>At first sight, it seems reasonable.(seems)</li> <li>It takes <strong>40 bytes</strong> from input, but it also <strong>puts NULL byte at the end of input.</strong></li> <li>Therefore, it has <strong>one-byte-overflow</strong>.</li> <li><strong>pwnable</strong></li> </ul> </li> <li> <p dir="auto"><code>scanf("%d", &num)</code></p> <ul dir="auto"> <li>Used with <code>alloca(num)</code> <ul dir="auto"> <li>Since <code>alloca</code> allocates memory from the stack frame of the caller, there is an instruction <code>sub esp, eax</code> to achieve that.</li> <li>If we make num negative, it will have overlapped stack frame.</li> <li>E.g. <a href="https://github.com/ctfs/write-ups-2016/tree/master/seccon-ctf-quals-2016/exploit/cheer-msg-100">Seccon CTF quals 2016 cheer_msg</a></li> </ul> </li> <li>Use num to access some data structures <ul dir="auto"> <li>In most of the time, programs only check the higher bound and forget to make num unsigned.</li> <li>Making num negative may let us overwrite some important data to control the world!</li> </ul> </li> </ul> </li> </ul> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">gets</h3><a id="user-content-gets" class="anchor" aria-label="Permalink: gets" href="#gets"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li> <p dir="auto"><code>gets(buf)</code></p> <ul dir="auto"> <li>No boundary check.</li> <li><strong>pwnable</strong></li> </ul> </li> <li> <p dir="auto"><code>fgets(buf, 40, stdin)</code></p> <ul dir="auto"> <li>It takes only <strong>39 bytes</strong> from the input and puts NULL byte at the end of input.</li> <li><strong>useless</strong></li> </ul> </li> </ul> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">read</h3><a id="user-content-read" class="anchor" aria-label="Permalink: read" href="#read"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li><code>read(stdin, buf, 40)</code> <ul dir="auto"> <li>It takes <strong>40 bytes</strong> from the input, and it doesn't put NULL byte at the end of input.</li> <li>It seems safe, but it may have <strong>information leak</strong>.</li> <li><strong>leakable</strong></li> </ul> </li> </ul> <p dir="auto">E.g.</p> <p dir="auto"><strong>memory layout</strong></p> <div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="0x7fffffffdd00: 0x4141414141414141 0x4141414141414141 0x7fffffffdd10: 0x4141414141414141 0x4141414141414141 0x7fffffffdd20: 0x4141414141414141 0x00007fffffffe1cd"><pre class="notranslate"><code>0x7fffffffdd00: 0x4141414141414141 0x4141414141414141 0x7fffffffdd10: 0x4141414141414141 0x4141414141414141 0x7fffffffdd20: 0x4141414141414141 0x00007fffffffe1cd </code></pre></div> <ul dir="auto"> <li> <p dir="auto">If there is a <code>printf</code> or <code>puts</code> used to output the buf, it will keep outputting until reaching NULL byte.</p> </li> <li> <p dir="auto">In this case, we can get <code>'A'*40 + '\xcd\xe1\xff\xff\xff\x7f'</code>.</p> </li> <li> <p dir="auto"><code>fread(buf, 1, 40, stdin)</code></p> <ul dir="auto"> <li>Almost the same as <code>read</code>.</li> <li><strong>leakable</strong></li> </ul> </li> </ul> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">strcpy</h3><a id="user-content-strcpy" class="anchor" aria-label="Permalink: strcpy" href="#strcpy"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">Assume that there is another buffer: <code>char buf2[60]</code></p> <ul dir="auto"> <li> <p dir="auto"><code>strcpy(buf, buf2)</code></p> <ul dir="auto"> <li>No boundary check.</li> <li>It copies the content of buf2(until reaching NULL byte) which may be longer than <code>length(buf)</code> to buf.</li> <li>Therefore, it may happen overflow.</li> <li><strong>pwnable</strong></li> </ul> </li> <li> <p dir="auto"><code>strncpy(buf, buf2, 40)</code> && <code>memcpy(buf, buf2, 40)</code></p> <ul dir="auto"> <li>It copies 40 bytes from buf2 to buf, but it won't put NULL byte at the end.</li> <li>Since there is no NULL byte to terminate, it may have <strong>information leak</strong>.</li> <li><strong>leakable</strong></li> </ul> </li> </ul> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">strcat</h3><a id="user-content-strcat" class="anchor" aria-label="Permalink: strcat" href="#strcat"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">Assume that there is another buffer: <code>char buf2[60]</code></p> <ul dir="auto"> <li> <p dir="auto"><code>strcat(buf, buf2)</code></p> <ul dir="auto"> <li>Of course, it may cause <strong>overflow</strong> if <code>length(buf)</code> isn't large enough.</li> <li>It puts NULL byte at the end, it may cause <strong>one-byte-overflow</strong>.</li> <li>In some cases, we can use this NULL byte to change stack address or heap address.</li> <li><strong>pwnable</strong></li> </ul> </li> <li> <p dir="auto"><code>strncat(buf, buf2, n)</code></p> <ul dir="auto"> <li>Almost the same as <code>strcat</code>, but with size limitation.</li> <li><strong>pwnable</strong></li> <li>E.g. <a href="https://github.com/ctfs/write-ups-2016/tree/master/seccon-ctf-quals-2016/exploit/jmper-300">Seccon CTF quals 2016 jmper</a></li> </ul> </li> </ul> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Find string in gdb</h2><a id="user-content-find-string-in-gdb" class="anchor" aria-label="Permalink: Find string in gdb" href="#find-string-in-gdb"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">In the problem of <a href="http://j00ru.vexillium.org/blog/24_03_15/dragons_ctf.pdf" rel="nofollow">SSP</a>, we need to find out the offset between <code>argv[0]</code> and the input buffer.</p> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">gdb</h3><a id="user-content-gdb" class="anchor" aria-label="Permalink: gdb" href="#gdb"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li>Use <code>p/x ((char **)environ)</code> in gdb, and the address of argv[0] will be the <code>output - 0x10</code></li> </ul> <p dir="auto">E.g.</p> <div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="(gdb) p/x (char **)environ $9 = 0x7fffffffde38 (gdb) x/gx 0x7fffffffde38-0x10 0x7fffffffde28: 0x00007fffffffe1cd (gdb) x/s 0x00007fffffffe1cd 0x7fffffffe1cd: "/home/naetw/CTF/seccon2016/check/checker""><pre class="notranslate"><code>(gdb) p/x (char **)environ $9 = 0x7fffffffde38 (gdb) x/gx 0x7fffffffde38-0x10 0x7fffffffde28: 0x00007fffffffe1cd (gdb) x/s 0x00007fffffffe1cd 0x7fffffffe1cd: "/home/naetw/CTF/seccon2016/check/checker" </code></pre></div> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto"><a href="https://github.com/longld/peda">gdb peda</a></h3><a id="user-content-gdb-peda" class="anchor" aria-label="Permalink: gdb peda" href="#gdb-peda"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li>Use <code>searchmem "/home/naetw/CTF/seccon2016/check/checker"</code></li> <li>Then use <code>searchmem $result_address</code></li> </ul> <div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="gdb-peda$ searchmem "/home/naetw/CTF/seccon2016/check/checker" Searching for '/home/naetw/CTF/seccon2016/check/checker' in: None ranges Found 3 results, display max 3 items: [stack] : 0x7fffffffe1cd ("/home/naetw/CTF/seccon2016/check/checker") [stack] : 0x7fffffffed7c ("/home/naetw/CTF/seccon2016/check/checker") [stack] : 0x7fffffffefcf ("/home/naetw/CTF/seccon2016/check/checker") gdb-peda$ searchmem 0x7fffffffe1cd Searching for '0x7fffffffe1cd' in: None ranges Found 2 results, display max 2 items: libc : 0x7ffff7dd33b8 --> 0x7fffffffe1cd ("/home/naetw/CTF/seccon2016/check/checker") [stack] : 0x7fffffffde28 --> 0x7fffffffe1cd ("/home/naetw/CTF/seccon2016/check/checker")"><pre class="notranslate"><code>gdb-peda$ searchmem "/home/naetw/CTF/seccon2016/check/checker" Searching for '/home/naetw/CTF/seccon2016/check/checker' in: None ranges Found 3 results, display max 3 items: [stack] : 0x7fffffffe1cd ("/home/naetw/CTF/seccon2016/check/checker") [stack] : 0x7fffffffed7c ("/home/naetw/CTF/seccon2016/check/checker") [stack] : 0x7fffffffefcf ("/home/naetw/CTF/seccon2016/check/checker") gdb-peda$ searchmem 0x7fffffffe1cd Searching for '0x7fffffffe1cd' in: None ranges Found 2 results, display max 2 items: libc : 0x7ffff7dd33b8 --> 0x7fffffffe1cd ("/home/naetw/CTF/seccon2016/check/checker") [stack] : 0x7fffffffde28 --> 0x7fffffffe1cd ("/home/naetw/CTF/seccon2016/check/checker") </code></pre></div> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Binary Service</h2><a id="user-content-binary-service" class="anchor" aria-label="Permalink: Binary Service" href="#binary-service"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">Normal:</p> <ul dir="auto"> <li><code>ncat -vc ./binary -kl 127.0.0.1 $port</code></li> </ul> <p dir="auto">With specific library in two ways:</p> <ul dir="auto"> <li><code>ncat -vc 'LD_PRELOAD=/path/to/libc.so ./binary' -kl 127.0.0.1 $port</code></li> <li><code>ncat -vc 'LD_LIBRARY_PATH=/path/of/libc.so ./binary' -kl 127.0.0.1 $port</code></li> </ul> <p dir="auto">After this, you can connect to binary service by command <code>nc localhost $port</code>.</p> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Find specific function offset in libc</h2><a id="user-content-find-specific-function-offset-in-libc" class="anchor" aria-label="Permalink: Find specific function offset in libc" href="#find-specific-function-offset-in-libc"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">If we leaked libc address of certain function successfully, we could use get libc base address by subtracting the offset of that function.</p> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">Manually</h3><a id="user-content-manually" class="anchor" aria-label="Permalink: Manually" href="#manually"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li><code>readelf -s $libc | grep ${function}@</code></li> </ul> <p dir="auto">E.g.</p> <div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="$ readelf -s libc-2.19.so | grep system@ 620: 00040310 56 FUNC GLOBAL DEFAULT 12 __libc_system@@GLIBC_PRIVATE 1443: 00040310 56 FUNC WEAK DEFAULT 12 system@@GLIBC_2.0"><pre class="notranslate"><code>$ readelf -s libc-2.19.so | grep system@ 620: 00040310 56 FUNC GLOBAL DEFAULT 12 __libc_system@@GLIBC_PRIVATE 1443: 00040310 56 FUNC WEAK DEFAULT 12 system@@GLIBC_2.0 </code></pre></div> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">Automatically</h3><a id="user-content-automatically" class="anchor" aria-label="Permalink: Automatically" href="#automatically"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li>Use <a href="https://github.com/Gallopsled/pwntools">pwntools</a>, then you can use it in your exploit script.</li> </ul> <p dir="auto">E.g.</p> <div class="highlight highlight-source-python notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="from pwn import * libc = ELF('libc.so') system_off = libc.symbols['system']"><pre><span class="pl-k">from</span> <span class="pl-s1">pwn</span> <span class="pl-k">import</span> <span class="pl-c1">*</span> <span class="pl-s1">libc</span> <span class="pl-c1">=</span> <span class="pl-en">ELF</span>(<span class="pl-s">'libc.so'</span>) <span class="pl-s1">system_off</span> <span class="pl-c1">=</span> <span class="pl-s1">libc</span>.<span class="pl-c1">symbols</span>[<span class="pl-s">'system'</span>]</pre></div> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Find '/bin/sh' or 'sh' in library</h2><a id="user-content-find-binsh-or-sh-in-library" class="anchor" aria-label="Permalink: Find '/bin/sh' or 'sh' in library" href="#find-binsh-or-sh-in-library"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">Need libc base address first</p> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">Manually</h3><a id="user-content-manually-1" class="anchor" aria-label="Permalink: Manually" href="#manually-1"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li><code>objdump -s libc.so | less</code> then search 'sh'</li> <li><code>strings -tx libc.so | grep /bin/sh</code></li> </ul> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">Automatically</h3><a id="user-content-automatically-1" class="anchor" aria-label="Permalink: Automatically" href="#automatically-1"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li>Use <a href="https://github.com/Gallopsled/pwntools">pwntools</a></li> </ul> <p dir="auto">E.g.</p> <div class="highlight highlight-source-python notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="from pwn import * libc = ELF('libc.so') ... sh = base + next(libc.search('sh\x00')) binsh = base + next(libc.search('/bin/sh\x00'))"><pre><span class="pl-k">from</span> <span class="pl-s1">pwn</span> <span class="pl-k">import</span> <span class="pl-c1">*</span> <span class="pl-s1">libc</span> <span class="pl-c1">=</span> <span class="pl-en">ELF</span>(<span class="pl-s">'libc.so'</span>) ... <span class="pl-s1">sh</span> <span class="pl-c1">=</span> <span class="pl-s1">base</span> <span class="pl-c1">+</span> <span class="pl-en">next</span>(<span class="pl-s1">libc</span>.<span class="pl-c1">search</span>(<span class="pl-s">'sh<span class="pl-cce">\x00</span>'</span>)) <span class="pl-s1">binsh</span> <span class="pl-c1">=</span> <span class="pl-s1">base</span> <span class="pl-c1">+</span> <span class="pl-en">next</span>(<span class="pl-s1">libc</span>.<span class="pl-c1">search</span>(<span class="pl-s">'/bin/sh<span class="pl-cce">\x00</span>'</span>))</pre></div> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Leak stack address</h2><a id="user-content-leak-stack-address" class="anchor" aria-label="Permalink: Leak stack address" href="#leak-stack-address"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto"><strong>constraints</strong>:</p> <ul dir="auto"> <li>Have already leaked libc base address</li> <li>Can leak the content of arbitrary address</li> </ul> <p dir="auto">There is a symbol <code>environ</code> in libc, whose value is the same as the third argument of <code>main</code> function, <code>char **envp</code>. The value of <code>char **envp</code> is on the stack, thus we can leak stack address with this symbol.</p> <div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="(gdb) list 1 1 #include <stdlib.h> 2 #include <stdio.h> 3 4 extern char **environ; 5 6 int main(int argc, char **argv, char **envp) 7 { 8 return 0; 9 } (gdb) x/gx 0x7ffff7a0e000 + 0x3c5f38 0x7ffff7dd3f38 <environ>: 0x00007fffffffe230 (gdb) p/x (char **)envp $12 = 0x7fffffffe230"><pre class="notranslate"><code>(gdb) list 1 1 #include <stdlib.h> 2 #include <stdio.h> 3 4 extern char **environ; 5 6 int main(int argc, char **argv, char **envp) 7 { 8 return 0; 9 } (gdb) x/gx 0x7ffff7a0e000 + 0x3c5f38 0x7ffff7dd3f38 <environ>: 0x00007fffffffe230 (gdb) p/x (char **)envp $12 = 0x7fffffffe230 </code></pre></div> <ul dir="auto"> <li><code>0x7ffff7a0e000</code> is current libc base address</li> <li><code>0x3c5f38</code> is offset of <code>environ</code> in libc</li> </ul> <p dir="auto">This <a href="https://www.gnu.org/software/libc/manual/html_node/Program-Arguments.html" rel="nofollow">manual</a> explains details about <code>environ</code>.</p> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Fork problem in gdb</h2><a id="user-content-fork-problem-in-gdb" class="anchor" aria-label="Permalink: Fork problem in gdb" href="#fork-problem-in-gdb"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">When you use <strong>gdb</strong> to debug a binary with <code>fork()</code> function, you can use the following command to determine which process to follow (The default setting of original gdb is parent, while that of gdb-peda is child.):</p> <ul dir="auto"> <li><code>set follow-fork-mode parent</code></li> <li><code>set follow-fork-mode child</code></li> </ul> <p dir="auto">Alternatively, using <code>set detach-on-fork off</code>, we can then control both sides of each fork. Using <code>inferior X</code> where <code>X</code> is any of the numbers that show up for <code>info inferiors</code> will switch to that side of the fork. This is useful if both sides of the fork are necessary to attack a challenge, and the simple <code>follow</code> ones above aren't sufficient.</p> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Secret of a mysterious section - .tls</h2><a id="user-content-secret-of-a-mysterious-section---tls" class="anchor" aria-label="Permalink: Secret of a mysterious section - .tls" href="#secret-of-a-mysterious-section---tls"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto"><strong>constraints</strong>:</p> <ul dir="auto"> <li>Need <code>malloc</code> function and you can malloc with arbitrary size</li> <li>Arbitrary address leaking</li> </ul> <p dir="auto">We make <code>malloc</code> use <code>mmap</code> to allocate memory(size 0x21000 is enough). In general, these pages will be placed at the address just before <code>.tls</code> section.</p> <p dir="auto">There is some useful information on <strong><code>.tls</code></strong>, such as the address of <code>main_arena</code>, <code>canary</code> (value of stack guard), and a strange <code>stack address</code> which points to somewhere on the stack but with a fixed offset.</p> <p dir="auto"><strong>Before calling mmap:</strong></p> <div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="7fecbfe4d000-7fecbfe51000 r--p 001bd000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so 7fecbfe51000-7fecbfe53000 rw-p 001c1000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so 7fecbfe53000-7fecbfe57000 rw-p 00000000 00:00 0 7fecbfe57000-7fecbfe7c000 r-xp 00000000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so 7fecc0068000-7fecc006a000 rw-p 00000000 00:00 0 <- .tls section 7fecc0078000-7fecc007b000 rw-p 00000000 00:00 0 7fecc007b000-7fecc007c000 r--p 00024000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so 7fecc007c000-7fecc007d000 rw-p 00025000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so"><pre class="notranslate"><code>7fecbfe4d000-7fecbfe51000 r--p 001bd000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so 7fecbfe51000-7fecbfe53000 rw-p 001c1000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so 7fecbfe53000-7fecbfe57000 rw-p 00000000 00:00 0 7fecbfe57000-7fecbfe7c000 r-xp 00000000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so 7fecc0068000-7fecc006a000 rw-p 00000000 00:00 0 <- .tls section 7fecc0078000-7fecc007b000 rw-p 00000000 00:00 0 7fecc007b000-7fecc007c000 r--p 00024000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so 7fecc007c000-7fecc007d000 rw-p 00025000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so </code></pre></div> <p dir="auto"><strong>After call mmap:</strong></p> <div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="7fecbfe4d000-7fecbfe51000 r--p 001bd000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so 7fecbfe51000-7fecbfe53000 rw-p 001c1000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so 7fecbfe53000-7fecbfe57000 rw-p 00000000 00:00 0 7fecbfe57000-7fecbfe7c000 r-xp 00000000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so 7fecc0045000-7fecc006a000 rw-p 00000000 00:00 0 <- memory of mmap + .tls section 7fecc0078000-7fecc007b000 rw-p 00000000 00:00 0 7fecc007b000-7fecc007c000 r--p 00024000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so 7fecc007c000-7fecc007d000 rw-p 00025000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so"><pre class="notranslate"><code>7fecbfe4d000-7fecbfe51000 r--p 001bd000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so 7fecbfe51000-7fecbfe53000 rw-p 001c1000 fd:00 131210 /lib/x86_64-linux-gnu/libc-2.24.so 7fecbfe53000-7fecbfe57000 rw-p 00000000 00:00 0 7fecbfe57000-7fecbfe7c000 r-xp 00000000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so 7fecc0045000-7fecc006a000 rw-p 00000000 00:00 0 <- memory of mmap + .tls section 7fecc0078000-7fecc007b000 rw-p 00000000 00:00 0 7fecc007b000-7fecc007c000 r--p 00024000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so 7fecc007c000-7fecc007d000 rw-p 00025000 fd:00 131206 /lib/x86_64-linux-gnu/ld-2.24.so </code></pre></div> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Predictable RNG(Random Number Generator)</h2><a id="user-content-predictable-rngrandom-number-generator" class="anchor" aria-label="Permalink: Predictable RNG(Random Number Generator)" href="#predictable-rngrandom-number-generator"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">When the binary uses the RNG to make the address of important information or sth, we can guess the same value if it's predictable.</p> <p dir="auto">Assuming that it's predictable, we can use <a href="https://docs.python.org/2/library/ctypes.html" rel="nofollow">ctypes</a> which is a build-in module in Python.</p> <p dir="auto"><strong>ctypes</strong> allows calling a function in DLL(Dynamic-Link Library) or Shared Library.</p> <p dir="auto">Therefore, if binary has an init_proc like this:</p> <div class="highlight highlight-source-c notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="srand(time(NULL)); while(addr <= 0x10000){ addr = rand() & 0xfffff000; } secret = mmap(addr,0x1000,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANONYMOUS ,-1,0); if(secret == -1){ puts("mmap error"); exit(0); }"><pre><span class="pl-en">srand</span>(<span class="pl-en">time</span>(<span class="pl-c1">NULL</span>)); <span class="pl-k">while</span>(<span class="pl-s1">addr</span> <= <span class="pl-c1">0x10000</span>){ <span class="pl-s1">addr</span> <span class="pl-c1">=</span> <span class="pl-en">rand</span>() <span class="pl-c1">&</span> <span class="pl-c1">0xfffff000</span>; } <span class="pl-s1">secret</span> <span class="pl-c1">=</span> <span class="pl-en">mmap</span>(<span class="pl-s1">addr</span>,<span class="pl-c1">0x1000</span>,<span class="pl-c1">PROT_READ</span>|<span class="pl-c1">PROT_WRITE</span>,<span class="pl-c1">MAP_PRIVATE</span>|<span class="pl-c1">MAP_ANONYMOUS</span> ,<span class="pl-c1">-1</span>,<span class="pl-c1">0</span>); <span class="pl-k">if</span>(<span class="pl-s1">secret</span> <span class="pl-c1">==</span> <span class="pl-c1">-1</span>){ <span class="pl-en">puts</span>(<span class="pl-s">"mmap error"</span>); <span class="pl-en">exit</span>(<span class="pl-c1">0</span>); }</pre></div> <p dir="auto">Then we can use <strong>ctypes</strong> to get the same value of addr.</p> <div class="highlight highlight-source-python notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="import ctypes LIBC = ctypes.cdll.LoadLibrary('/path/to/dll') LIBC.srand(LIBC.time(0)) addr = LIBC.rand() & 0xfffff000"><pre><span class="pl-k">import</span> <span class="pl-s1">ctypes</span> <span class="pl-c1">LIBC</span> <span class="pl-c1">=</span> <span class="pl-s1">ctypes</span>.<span class="pl-c1">cdll</span>.<span class="pl-c1">LoadLibrary</span>(<span class="pl-s">'/path/to/dll'</span>) <span class="pl-c1">LIBC</span>.<span class="pl-c1">srand</span>(<span class="pl-c1">LIBC</span>.<span class="pl-c1">time</span>(<span class="pl-c1">0</span>)) <span class="pl-s1">addr</span> <span class="pl-c1">=</span> <span class="pl-c1">LIBC</span>.<span class="pl-c1">rand</span>() <span class="pl-c1">&</span> <span class="pl-c1">0xfffff000</span></pre></div> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Make stack executable</h2><a id="user-content-make-stack-executable" class="anchor" aria-label="Permalink: Make stack executable" href="#make-stack-executable"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li><a href="http://radare.today/posts/defeating-baby_rop-with-radare2/" rel="nofollow">link1</a></li> <li><a href="https://sploitfun.wordpress.com/author/sploitfun/" rel="nofollow">link2</a></li> <li>Haven't read yet orz</li> </ul> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Use one-gadget-RCE instead of system</h2><a id="user-content-use-one-gadget-rce-instead-of-system" class="anchor" aria-label="Permalink: Use one-gadget-RCE instead of system" href="#use-one-gadget-rce-instead-of-system"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto"><strong>constraints</strong>:</p> <ul dir="auto"> <li>Have libc base address</li> <li>Write to arbitrary address</li> </ul> <p dir="auto">Almost every pwnable challenge needs to call <code>system('/bin/sh')</code> in the end of the exploit, but if we want to call that, we have to manipulate the parameters and, of course, hijack some functions to <code>system</code>. What if we <strong>can't</strong> manipulate the parameter?</p> <p dir="auto">Use <a href="http://j00ru.vexillium.org/blog/24_03_15/dragons_ctf.pdf" rel="nofollow">one-gadget-RCE</a>!</p> <p dir="auto">With <strong>one-gadget-RCE</strong>, we can just hijack <code>.got.plt</code> or something we can use to control eip to make program jump to <strong>one-gadget</strong>, but there are some constraints that need satisfying before using it.</p> <p dir="auto">There are lots of <strong>one-gadgets</strong> in libc. Each one has different constraints but those are similar. Each constraint is about the state of registers.</p> <p dir="auto">E.g.</p> <ul dir="auto"> <li>ebx is the address of <code>rw-p</code> area of libc</li> <li>[esp+0x34] == NULL</li> </ul> <p dir="auto">How can we get these constraints? Here is an useful tool <a href="https://github.com/david942j/one_gadget">one_gadget</a> !!!!</p> <p dir="auto">So if we can satisfy those constraints, we can get the shell more easily.</p> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Hijack hook function</h2><a id="user-content-hijack-hook-function" class="anchor" aria-label="Permalink: Hijack hook function" href="#hijack-hook-function"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto"><strong>constraints</strong>:</p> <ul dir="auto"> <li>Have libc base address</li> <li>Write to arbitrary address</li> <li>The program uses <code>malloc</code>, <code>free</code> or <code>realloc</code>.</li> </ul> <p dir="auto">By manual:</p> <blockquote> <p dir="auto">The GNU C Library lets you modify the behavior of <code>malloc</code>, <code>realloc</code>, and <code>free</code> by specifying appropriate hook functions. You can use these hooks to help you debug programs that use dynamic memory allocation, for example.</p> </blockquote> <p dir="auto">There are hook variables declared in malloc.h and their default values are <code>0x0</code>.</p> <ul dir="auto"> <li><code>__malloc_hook</code></li> <li><code>__free_hook</code></li> <li>...</li> </ul> <p dir="auto">Since they are used to help us debug programs, they are writable during the execution.</p> <div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="0xf77228e0 <__free_hook>: 0x00000000 0xf7722000 0xf7727000 rw-p mapped"><pre class="notranslate"><code>0xf77228e0 <__free_hook>: 0x00000000 0xf7722000 0xf7727000 rw-p mapped </code></pre></div> <p dir="auto">Let's look into the <a href="https://code.woboq.org/userspace/glibc/malloc/malloc.c.html#2917" rel="nofollow">src</a> of malloc.c. I will use <code>__libc_free</code> to demo.</p> <div class="highlight highlight-source-c notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="void (*hook) (void *, const void *) = atomic_forced_read (__free_hook); if (__builtin_expect (hook != NULL, 0)) { (*hook)(mem, RETURN_ADDRESS (0)); return; }"><pre><span class="pl-smi">void</span> (<span class="pl-c1">*</span><span class="pl-s1">hook</span>) (<span class="pl-smi">void</span> <span class="pl-c1">*</span>, <span class="pl-k">const</span> <span class="pl-smi">void</span> <span class="pl-c1">*</span>) <span class="pl-c1">=</span> <span class="pl-en">atomic_forced_read</span> (<span class="pl-s1">__free_hook</span>); <span class="pl-k">if</span> (<span class="pl-en">__builtin_expect</span> (<span class="pl-s1">hook</span> <span class="pl-c1">!=</span> <span class="pl-c1">NULL</span>, <span class="pl-c1">0</span>)) { (<span class="pl-c1">*</span><span class="pl-s1">hook</span>)(<span class="pl-s1">mem</span>, <span class="pl-en">RETURN_ADDRESS</span> (<span class="pl-c1">0</span>)); <span class="pl-k">return</span>; }</pre></div> <p dir="auto">It checks the value of <code>__free_hook</code>. If it's not NULL, it will call the hook function first. Here, we would like to use <strong>one-gadget-RCE</strong>. Since hook function is called in the libc, the constraints of <strong>one-gadget</strong> are usually satisfied.</p> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Use printf to trigger malloc and free</h2><a id="user-content-use-printf-to-trigger-malloc-and-free" class="anchor" aria-label="Permalink: Use printf to trigger malloc and free" href="#use-printf-to-trigger-malloc-and-free"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">Look into the source of printf, there are several places which may trigger malloc. Take <a href="https://code.woboq.org/userspace/glibc/stdio-common/vfprintf.c.html#1470" rel="nofollow">vfprintf.c line 1470</a> for example:</p> <div class="highlight highlight-source-c notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="#define EXTSIZ 32 enum { WORK_BUFFER_SIZE = 1000 }; if (width >= WORK_BUFFER_SIZE - EXTSIZ) { /* We have to use a special buffer. */ size_t needed = ((size_t) width + EXTSIZ) * sizeof (CHAR_T); if (__libc_use_alloca (needed)) workend = (CHAR_T *) alloca (needed) + width + EXTSIZ; else { workstart = (CHAR_T *) malloc (needed); if (workstart == NULL) { done = -1; goto all_done; } workend = workstart + width + EXTSIZ; } }"><pre><span class="pl-k">#define</span> <span class="pl-c1">EXTSIZ</span> 32 <span class="pl-k">enum</span> { <span class="pl-c1">WORK_BUFFER_SIZE</span> <span class="pl-c1">=</span> <span class="pl-c1">1000</span> }; <span class="pl-k">if</span> (<span class="pl-s1">width</span> >= <span class="pl-c1">WORK_BUFFER_SIZE</span> <span class="pl-c1">-</span> <span class="pl-c1">EXTSIZ</span>) { <span class="pl-c">/* We have to use a special buffer. */</span> <span class="pl-smi">size_t</span> <span class="pl-s1">needed</span> <span class="pl-c1">=</span> ((<span class="pl-smi">size_t</span>) <span class="pl-s1">width</span> <span class="pl-c1">+</span> <span class="pl-c1">EXTSIZ</span>) <span class="pl-c1">*</span> <span class="pl-k">sizeof</span> (<span class="pl-c1">CHAR_T</span>); <span class="pl-k">if</span> (<span class="pl-en">__libc_use_alloca</span> (<span class="pl-s1">needed</span>)) <span class="pl-s1">workend</span> <span class="pl-c1">=</span> (<span class="pl-smi">CHAR_T</span> <span class="pl-c1">*</span>) <span class="pl-en">alloca</span> (<span class="pl-s1">needed</span>) <span class="pl-c1">+</span> <span class="pl-s1">width</span> <span class="pl-c1">+</span> <span class="pl-c1">EXTSIZ</span>; <span class="pl-k">else</span> { <span class="pl-s1">workstart</span> <span class="pl-c1">=</span> (<span class="pl-smi">CHAR_T</span> <span class="pl-c1">*</span>) <span class="pl-en">malloc</span> (<span class="pl-s1">needed</span>); <span class="pl-k">if</span> (<span class="pl-s1">workstart</span> <span class="pl-c1">==</span> <span class="pl-c1">NULL</span>) { <span class="pl-s1">done</span> <span class="pl-c1">=</span> <span class="pl-c1">-1</span>; goto <span class="pl-ent">all_done</span>; } <span class="pl-s1">workend</span> <span class="pl-c1">=</span> <span class="pl-s1">workstart</span> <span class="pl-c1">+</span> <span class="pl-s1">width</span> <span class="pl-c1">+</span> <span class="pl-c1">EXTSIZ</span>; } }</pre></div> <p dir="auto">We can find that <code>malloc</code> will be triggered if the width field is large enough.(Of course, <code>free</code> will also be triggered at the end of printf if <code>malloc</code> has been triggered.) However, WORK_BUFFER_SIZE is not large enough, since we need to go to <strong>else</strong> block. Let's take a look at <code>__libc_use_alloca</code> and see what exactly the minimum size of width we should give.</p> <div class="highlight highlight-source-c notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content=" /* Minimum size for a thread. We are free to choose a reasonable value. */ #define PTHREAD_STACK_MIN 16384 #define __MAX_ALLOCA_CUTOFF 65536 int __libc_use_alloca (size_t size) { return (__builtin_expect (size <= PTHREAD_STACK_MIN / 4, 1) || __builtin_expect (__libc_alloca_cutoff (size), 1)); } int __libc_alloca_cutoff (size_t size) { return size <= (MIN (__MAX_ALLOCA_CUTOFF, THREAD_GETMEM (THREAD_SELF, stackblock_size) / 4 /* The main thread, before the thread library is initialized, has zero in the stackblock_size element. Since it is the main thread we can assume the maximum available stack space. */ ?: __MAX_ALLOCA_CUTOFF * 4)); }"><pre><span class="pl-c">/* Minimum size for a thread. We are free to choose a reasonable value. */</span> <span class="pl-k">#define</span> <span class="pl-c1">PTHREAD_STACK_MIN</span> 16384 <span class="pl-k">#define</span> <span class="pl-s1">__MAX_ALLOCA_CUTOFF</span> 65536 <span class="pl-smi">int</span> <span class="pl-en">__libc_use_alloca</span> (<span class="pl-smi">size_t</span> <span class="pl-s1">size</span>) { <span class="pl-k">return</span> (<span class="pl-en">__builtin_expect</span> (<span class="pl-s1">size</span> <= <span class="pl-c1">PTHREAD_STACK_MIN</span> / <span class="pl-c1">4</span>, <span class="pl-c1">1</span>) <span class="pl-c1">||</span> <span class="pl-en">__builtin_expect</span> (<span class="pl-en">__libc_alloca_cutoff</span> (<span class="pl-s1">size</span>), <span class="pl-c1">1</span>)); } <span class="pl-smi">int</span> <span class="pl-en">__libc_alloca_cutoff</span> (<span class="pl-smi">size_t</span> <span class="pl-s1">size</span>) { <span class="pl-k">return</span> <span class="pl-s1">size</span> <= (<span class="pl-en">MIN</span> (<span class="pl-s1">__MAX_ALLOCA_CUTOFF</span>, <span class="pl-en">THREAD_GETMEM</span> (<span class="pl-c1">THREAD_SELF</span>, <span class="pl-s1">stackblock_size</span>) / <span class="pl-c1">4</span> <span class="pl-c">/* The main thread, before the thread library is</span> <span class="pl-c"> initialized, has zero in the stackblock_size</span> <span class="pl-c"> element. Since it is the main thread we can</span> <span class="pl-c"> assume the maximum available stack space. */</span> ?: <span class="pl-s1">__MAX_ALLOCA_CUTOFF</span> <span class="pl-c1">*</span> <span class="pl-c1">4</span>)); }</pre></div> <p dir="auto">We have to make sure that:</p> <ol dir="auto"> <li><code>size > PTHREAD_STACK_MIN / 4</code></li> <li><code>size > MIN(__MAX_ALLOCA_CUTOFF, THREAD_GETMEM(THREAD_SELF, stackblock_size) / 4 ?: __MAX_ALLOCA_CUTOFF * 4)</code> <ul dir="auto"> <li>I did not fully understand what exactly the function - THREAD_GETMEM do, but it seems that it mostly returns 0.</li> <li>Therefore, the second condition is usually <code>size > 65536</code></li> </ul> </li> </ol> <p dir="auto">More details:</p> <ul dir="auto"> <li><a href="https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html" rel="nofollow">__builtin_expect</a></li> <li><a href="https://code.woboq.org/userspace/glibc/sysdeps/x86_64/nptl/tls.h.html#_M/THREAD_GETMEM" rel="nofollow">THREAD_GETMEM</a></li> </ul> <div class="markdown-heading" dir="auto"><h3 tabindex="-1" class="heading-element" dir="auto">conclusion</h3><a id="user-content-conclusion" class="anchor" aria-label="Permalink: conclusion" href="#conclusion"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <ul dir="auto"> <li>The minimum size of width to trigger <code>malloc</code> & <code>free</code> is 65537 most of the time.</li> <li>If there is a Format String Vulnerability and the program ends right after calling <code>printf(buf)</code>, we can hijack <code>__malloc_hook</code> or <code>__free_hook</code> with <code>one-gadget</code> and use the trick mentioned above to trigger <code>malloc</code> & <code>free</code> then we can still get the shell even there is no more function call or sth after <code>printf(buf)</code>.</li> </ul> <div class="markdown-heading" dir="auto"><h2 tabindex="-1" class="heading-element" dir="auto">Use execveat to open a shell</h2><a id="user-content-use-execveat-to-open-a-shell" class="anchor" aria-label="Permalink: Use execveat to open a shell" href="#use-execveat-to-open-a-shell"><svg class="octicon octicon-link" viewBox="0 0 16 16" version="1.1" width="16" height="16" aria-hidden="true"><path d="m7.775 3.275 1.25-1.25a3.5 3.5 0 1 1 4.95 4.95l-2.5 2.5a3.5 3.5 0 0 1-4.95 0 .751.751 0 0 1 .018-1.042.751.751 0 0 1 1.042-.018 1.998 1.998 0 0 0 2.83 0l2.5-2.5a2.002 2.002 0 0 0-2.83-2.83l-1.25 1.25a.751.751 0 0 1-1.042-.018.751.751 0 0 1-.018-1.042Zm-4.69 9.64a1.998 1.998 0 0 0 2.83 0l1.25-1.25a.751.751 0 0 1 1.042.018.751.751 0 0 1 .018 1.042l-1.25 1.25a3.5 3.5 0 1 1-4.95-4.95l2.5-2.5a3.5 3.5 0 0 1 4.95 0 .751.751 0 0 1-.018 1.042.751.751 0 0 1-1.042.018 1.998 1.998 0 0 0-2.83 0l-2.5 2.5a1.998 1.998 0 0 0 0 2.83Z"></path></svg></a></div> <p dir="auto">When it comes to opening a shell with system call, <code>execve</code> always pops up in mind. However, it's not always easily available due to the lack of gadgets or others constraints.<br> Actually, there is a system call, <code>execveat</code>, with following prototype:</p> <div class="highlight highlight-source-c notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="int execveat(int dirfd, const char *pathname, char *const argv[], char *const envp[], int flags);"><pre><span class="pl-smi">int</span> <span class="pl-en">execveat</span>(<span class="pl-smi">int</span> <span class="pl-s1">dirfd</span>, <span class="pl-k">const</span> <span class="pl-smi">char</span> <span class="pl-c1">*</span><span class="pl-s1">pathname</span>, <span class="pl-smi">char</span> <span class="pl-c1">*</span><span class="pl-k">const</span> <span class="pl-s1">argv</span>[], <span class="pl-smi">char</span> <span class="pl-c1">*</span><span class="pl-k">const</span> <span class="pl-s1">envp</span>[], <span class="pl-smi">int</span> <span class="pl-s1">flags</span>);</pre></div> <p dir="auto">According to its <a href="http://man7.org/linux/man-pages/man2/execveat.2.html" rel="nofollow">man page</a>, it operates in the same way as <code>execve</code>. As for the additional arguments, it mentions that:</p> <blockquote> <p dir="auto">If pathname is absolute, then dirfd is ignored.</p> </blockquote> <p dir="auto">Hence, if we make <code>pathname</code> point to <code>"/bin/sh"</code>, and set <code>argv</code>, <code>envp</code> and <code>flags</code> to 0, we can still get a shell whatever the value of <code>dirfd</code>.</p> </article></div></div></div></div></div> <!-- --> <!-- --> <script type="application/json" id="__PRIMER_DATA_:R0:__">{"resolvedServerColorMode":"day"}</script></div> </react-partial> <input type="hidden" data-csrf="true" value="7x9slEOOIBxfHRgExn1cLISH9ZDm5U+vxQvApw9fxtnLA7p+hlhP7fTBjsWQv9fpVb0NVC5/3AKTM5F1142X2w==" /> </div> <div data-view-component="true" class="Layout-sidebar"> <div class="BorderGrid about-margin" data-pjax> <div class="BorderGrid-row"> <div class="BorderGrid-cell"> <div class="hide-sm hide-md"> <h2 class="mb-3 h4">About</h2> <p class="f4 my-3"> Here record some tips about pwn. 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