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href="https://hacks.mozilla.org/author/chollermozilla-com/">Christian Holler</a> </h2> <div class="post__meta"> Posted on <abbr class="published" title="2024-06-27T09:18:49-07:00"> June 27, 2024 </abbr> <span class="entry-cat">in <a href="https://hacks.mozilla.org/category/featured/" rel="category tag" title="View all posts in Featured Article" >Featured Article</a> and <a href="https://hacks.mozilla.org/category/firefox/" rel="category tag" title="View all posts in Firefox" >Firefox</a> </span> <div class="socialshare" data-type="bubbles"></div> </div> </div> </div> <main id="content-main" class="section article"> <article class="post" role="article"> <p><span style="font-weight: 400;">Process separation</span><span style="font-weight: 400;"> is one of the cornerstones of the Firefox security model. Instead of running Firefox as a single process, multiple processes with different privileges communicate with each other via </span><span style="font-weight: 400;">Inter-Process Communication</span><span style="font-weight: 400;"> (IPC). For example: loading a website, processing its resources, and rendering it is done by an isolated </span><span style="font-weight: 400;">Content Process</span><span style="font-weight: 400;"> with a very restrictive sandbox, whereas critical operations such as file system access are only allowed to be executed in the </span><span style="font-weight: 400;">Parent Process</span><span style="font-weight: 400;">. </span></p> <p><span style="font-weight: 400;">By running potentially harmful code with lower privileges, the impact of a potential code execution vulnerability is mitigated. In order to gain full control, the attacker now needs to find a second vulnerability that allows bypassing these privilege restrictions – which is colloquially known as a “</span><span style="font-weight: 400;">sandbox escape</span><span style="font-weight: 400;">”.</span></p> <p><span style="font-weight: 400;">In order to achieve a sandbox escape, an attacker essentially has two options: The first one is to directly attack the underlying operating system from within the compromised content process. Since every process needs to interact with the operating system for various tasks, an attacker can focus on finding bugs in these interfaces to elevate privileges. </span></p> <p><span style="font-weight: 400;">Since we have </span><a href="https://hacks.mozilla.org/2022/05/improved-process-isolation-in-firefox-100/"><span style="font-weight: 400;">already deployed</span></a><span style="font-weight: 400;"> changes to Firefox that severely limit the OS interfaces exposed to low-privilege processes, the second attack option becomes more interesting: Exploiting bugs in privileged IPC endpoints. Since low privilege content processes need to interact with the privileged parent process, the parent needs to expose certain interfaces.</span></p> <p><span style="font-weight: 400;"> If these interfaces do not perform the necessary security checks or contain memory safety errors, the content process might be able to exploit them and perform actions with higher privileges, possibly leading to an entire parent process takeover.</span></p> <p><span style="font-weight: 400;">Traditionally , fuzzing has had multiple success stories in the history of Mozilla and allowed us to find all sorts of problems including security vulnerabilities in our code. However, applying fuzzing to our critical IPC interfaces </span><a href="https://blog.mozilla.org/attack-and-defense/2021/01/27/effectively-fuzzing-the-ipc-layer-in-firefox/"><span style="font-weight: 400;">has historically always been difficult</span></a><span style="font-weight: 400;">. This is primarily because IPC interfaces cannot be tested in isolation, i.e. require the full browser for testing, and because incorrect usage of IPC interfaces can force browser restarts which introduce a prohibitive amount of latency between iterations. </span></p> <p><span style="font-weight: 400;">To find a solution to this challenge, we engaged with the research community to apply a new method of rewinding application state during fuzzing. We saw our first results with this approach in 2021 using an experimental prototype that would later become </span><a href="https://nyx-fuzz.com/"><span style="font-weight: 400;">the open source snapshot fuzzing tool called “Nyx”</span></a><span style="font-weight: 400;">.</span></p> <p><span style="font-weight: 400;">As of 2024, we are happy to announce that we are now running various </span><span style="font-weight: 400;">snapshot fuzzing</span><span style="font-weight: 400;"> targets for IPC in production. Snapshot fuzzing is a new technology that has become more popular in recent years and we are proud of our role in bringing it from concept to practicality. </span></p> <p><span style="font-weight: 400;">Using this technology we have already been able to identify and fix </span><a href="https://mzl.la/43JSNts"><span style="font-weight: 400;">a number of potential problems</span></a><span style="font-weight: 400;"> in our IPC layer and we will continue to improve our testing to provide you with the most secure version of Firefox.</span></p> <p><span style="font-weight: 400;">If you’d like to know more, or even consider contributing to Mozilla, check out </span><a href="https://blog.mozilla.org/attack-and-defense/2024/06/24/ipc-fuzzing-with-snapshots/"><span style="font-weight: 400;">our post on the security blog</span></a><span style="font-weight: 400;"> explaining the technical architecture behind this new tool.</span></p> <section class="about"> <h2 class="about__header">About Christian Holler </h3> <p>Christian is a Firefox Tech Lead and Principal Engineer at Mozilla.</p> <ul class="author-meta fa-ul"><li><i class="fa-li fa fa-twitter"></i><a href="http://twitter.com/mozdeco" class="twitter" rel="me">@mozdeco</a></li></ul> <p><a class="url" href="https://hacks.mozilla.org/author/chollermozilla-com/">More articles by Christian Holler…</a></p> </section> </article> <section class="promo"> <form id="newsletterForm" name="newsletter-form" class="newsletter block block--1 block--polite" action="https://www.mozilla.org/en-US/newsletter/" method="post"> <h2 class="heading">Discover great resources for web development</h2> <p class="newsletter__description">Sign up for the Mozilla Developer Newsletter:</p> <input id="fmt" name="fmt" value="H" type="hidden"> <input id="newsletterNewslettersInput" name="newsletters" value="app-dev" type="hidden"> <div id="newsletterErrors" class="newsletter__errors"></div> <div id="newsletterEmail" class="form__row"> <label for="newsletterEmailInput" class="offscreen">E-mail</label> <input id="newsletterEmailInput" name="email" class="newsletter__input" required="" placeholder="you@example.com" size="30" type="email"> </div> <div id="newsletterPrivacy" class="form__row form__fineprint"> <input id="newsletterPrivacyInput" name="privacy" required="" type="checkbox"> <label for="newsletterPrivacyInput"> I'm okay with Mozilla handling my info as explained in this <a href="https://www.mozilla.org/privacy/">Privacy Policy</a>. </label> </div> <button id="newsletter-submit" type="submit" class="button positive">Sign up now</button> </form> <div id="newsletterThanks" class="newsletter newsletter--thanks block block--1 block--polite hidden"> <h2 class="heading">Thanks! 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