PHP: User Submitted Data

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<option value='es/security.variables.php'>Spanish</option> <option value='fr/security.variables.php'>French</option> <option value='it/security.variables.php'>Italian</option> <option value='ja/security.variables.php'>Japanese</option> <option value='pt_BR/security.variables.php'>Brazilian Portuguese</option> <option value='ru/security.variables.php'>Russian</option> <option value='tr/security.variables.php'>Turkish</option> <option value='uk/security.variables.php'>Ukrainian</option> <option value='zh/security.variables.php'>Chinese (Simplified)</option> <option value='help-translate.php'>Other</option> </select> </fieldset> </form> </div> </div><div id="security.variables" class="chapter"> <h1 class="title">User Submitted Data</h1> <p class="para"> The greatest weakness in many <abbr title="PHP: Hypertext Preprocessor">PHP</abbr> programs is not inherent in the language itself, but merely an issue of code not being written with security in mind. For this reason, you should always take the time to consider the implications of a given piece of code, to ascertain the possible damage if an unexpected variable is submitted to it. <div class="example" id="example-465"> <p><strong>Example #1 Dangerous Variable Usage</strong></p> <div class="example-contents"> <div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// remove a file from the user's home directory... or maybe<br />// somebody else's?<br /></span><span style="color: #0000BB">unlink </span><span style="color: #007700">(</span><span style="color: #0000BB">$evil_var</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// Write logging of their access... or maybe an /etc/passwd entry?<br /></span><span style="color: #0000BB">fwrite </span><span style="color: #007700">(</span><span style="color: #0000BB">$fp</span><span style="color: #007700">, </span><span style="color: #0000BB">$evil_var</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// Execute something trivial.. or rm -rf *?<br /></span><span style="color: #0000BB">system </span><span style="color: #007700">(</span><span style="color: #0000BB">$evil_var</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">exec </span><span style="color: #007700">(</span><span style="color: #0000BB">$evil_var</span><span style="color: #007700">);<br /><br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> </p> <p class="para"> You should always carefully examine your code to make sure that any variables being submitted from a web browser are being properly checked, and ask yourself the following questions: <ul class="itemizedlist"> <li class="listitem"> <span class="simpara"> Will this script only affect the intended files? </span> </li> <li class="listitem"> <span class="simpara"> Can unusual or undesirable data be acted upon? </span> </li> <li class="listitem"> <span class="simpara"> Can this script be used in unintended ways? </span> </li> <li class="listitem"> <span class="simpara"> Can this be used in conjunction with other scripts in a negative manner? </span> </li> <li class="listitem"> <span class="simpara"> Will any transactions be adequately logged? </span> </li> </ul> </p> <p class="para"> By adequately asking these questions while writing the script, rather than later, you prevent an unfortunate re-write when you need to increase your security. By starting out with this mindset, you won't guarantee the security of your system, but you can help improve it. </p> <p class="para"> You may also want to consider turning off register_globals, magic_quotes, or other convenience settings which may confuse you as to the validity, source, or value of a given variable. Working with <abbr title="PHP: Hypertext Preprocessor">PHP</abbr> in error_reporting(E_ALL) mode can also help warn you about variables being used before they are checked or initialized (so you can prevent unusual data from being operated upon). </p> </div> <div class="contribute"> <h3 class="title">Improve This Page</h3> <div> </div> <div class="edit-bug"> <a href="https://github.com/php/doc-base/blob/master/README.md" title="This will take you to our contribution guidelines on GitHub" target="_blank" rel="noopener noreferrer">Learn How To Improve This Page</a> • <a href="https://github.com/php/doc-en/blob/master/security/variables.xml">Submit a Pull Request</a> • <a href="https://github.com/php/doc-en/issues/new?body=From%20manual%20page:%20https:%2F%2Fphp.net%2Fsecurity.variables%0A%0A---">Report a Bug</a> </div> </div><section id="usernotes"> <div class="head"> <span class="action"><a href="/manual/add-note.php?sect=security.variables&repo=en&redirect=https://www.php.net/manual/en/security.variables.php">＋<small>add a note</small></a></span> <h3 class="title">User Contributed Notes <span class="count">2 notes</span></h3> </div><div id="allnotes"> <div class="note" id="56715"> <div class="votes"> <div id="Vu56715"> <a href="/manual/vote-note.php?id=56715&page=security.variables&vote=up" title="Vote up!" class="usernotes-voteu">up</a> </div> <div id="Vd56715"> <a href="/manual/vote-note.php?id=56715&page=security.variables&vote=down" title="Vote down!" class="usernotes-voted">down</a> </div> <div class="tally" id="V56715" title="66% like this..."> 79 </div> </div> <a href="#56715" class="name"> <strong class="user"><em>Uli Kusterer</em></strong></a><a class="genanchor" href="#56715"> ¶</a><div class="date" title="2005-09-13 03:50"><strong>19 years ago</strong></div> <div class="text" id="Hcom56715"> <div class="phpcode"><code><span class="html">One thing I would repeat in the docs here is what information actually comes from the user. Many people think a Cookie, since it's written by PHP, was safe. But the fact is that it's stored on the user's computer, transferred by the user's browser, and thus very easy to manipulate.<br /><br />So, it'd be handy to mention here again that:<br /><br />CGI parameters in the URL, HTTP POST data and cookie variables are considered "user data" and thus need to be validated. Session data and SQL database contents only need to be validated if they came from untrustworthy sources (like the ones just mentioned).<br /><br />Not new, but I would have expected this info under this headline, at least as a short recap plus linlk to the actual docs.</span></code></div> </div> </div> <div class="note" id="80829"> <div class="votes"> <div id="Vu80829"> <a href="/manual/vote-note.php?id=80829&page=security.variables&vote=up" title="Vote up!" class="usernotes-voteu">up</a> </div> <div id="Vd80829"> <a href="/manual/vote-note.php?id=80829&page=security.variables&vote=down" title="Vote down!" class="usernotes-voted">down</a> </div> <div class="tally" id="V80829" title="52% like this..."> 6 </div> </div> <a href="#80829" class="name"> <strong class="user"><em>Livingstone@stonyhills[dot]com</em></strong></a><a class="genanchor" href="#80829"> ¶</a><div class="date" title="2008-02-02 04:51"><strong>16 years ago</strong></div> <div class="text" id="Hcom80829"> <div class="phpcode"><code><span class="html">making sure your form is submitted from your page! Could also be adapted to url, by additing &token to the query string and checking this against session data(or what ever array you like) with $_GET, not that this string is randomly generated and stored. If you like you could build your own array to store the generated string if you dont want to use $_SESSION, say you could make yours like $tokens = array(), and in your easysecure class you store all the stuff in that array!<br /><br /><span class="default"><?php<br /><br /></span><span class="keyword">class </span><span class="default">easysecure </span><span class="keyword">{<br /> <br /> var </span><span class="default">$curr_user</span><span class="keyword">;<br /> var </span><span class="default">$curr_permission</span><span class="keyword">;<br /> var </span><span class="default">$curr_task</span><span class="keyword">;<br /> var </span><span class="default">$validpermission</span><span class="keyword">;<br /> var </span><span class="default">$error</span><span class="keyword">;<br /> <br /> <br /> function &</span><span class="default">setVar</span><span class="keyword">( </span><span class="default">$name</span><span class="keyword">, </span><span class="default">$value</span><span class="keyword">=</span><span class="default">null </span><span class="keyword">) {<br /> if (!</span><span class="default">is_null</span><span class="keyword">( </span><span class="default">$value </span><span class="keyword">)) {<br /> </span><span class="default">$this</span><span class="keyword">-></span><span class="default">$name </span><span class="keyword">= </span><span class="default">$value</span><span class="keyword">;<br /> }<br /> return </span><span class="default">$this</span><span class="keyword">-></span><span class="default">$name</span><span class="keyword">;<br /> }<br /><br /> function </span><span class="default">maketoken</span><span class="keyword">(</span><span class="default">$formname</span><span class="keyword">, </span><span class="default">$id</span><span class="keyword">){<br /> <br /> </span><span class="default">$token </span><span class="keyword">= </span><span class="default">md5</span><span class="keyword">(</span><span class="default">uniqid</span><span class="keyword">(</span><span class="default">rand</span><span class="keyword">(), </span><span class="default">true</span><span class="keyword">));<br /> <br /> </span><span class="default">$_SESSION</span><span class="keyword">[</span><span class="default">$formname</span><span class="keyword">.</span><span class="default">$id</span><span class="keyword">] = </span><span class="default">$token</span><span class="keyword">;<br /> <br /> return </span><span class="default">$token</span><span class="keyword">;<br /> }<br /> <br /> function </span><span class="default">checktoken</span><span class="keyword">(</span><span class="default">$token</span><span class="keyword">, </span><span class="default">$formname</span><span class="keyword">, </span><span class="default">$id</span><span class="keyword">){<br /> </span><span class="comment">//print_r($_SESSION);<br /> //echo ($token);<br /> //if we dont have a valid token, return invalid;<br /> </span><span class="keyword">if(!</span><span class="default">$token</span><span class="keyword">){<br /> </span><span class="default">$this</span><span class="keyword">-></span><span class="default">setVar</span><span class="keyword">(</span><span class="string">'validpermission'</span><span class="keyword">, </span><span class="default">0</span><span class="keyword">);<br /> </span><span class="default">$this</span><span class="keyword">-></span><span class="default">setVar</span><span class="keyword">(</span><span class="string">'error'</span><span class="keyword">, </span><span class="string">'no token found, security bridgedetected'</span><span class="keyword">);<br /> return </span><span class="default">false</span><span class="keyword">;<br /> }<br /> <br /> </span><span class="comment">//if we have a valid token check that is is valid<br /> </span><span class="default">$key </span><span class="keyword">= </span><span class="default">$_SESSION</span><span class="keyword">[</span><span class="default">$formname</span><span class="keyword">.</span><span class="default">$id</span><span class="keyword">];<br /> if(</span><span class="default">$key </span><span class="keyword">!== </span><span class="default">$token </span><span class="keyword">){<br /> </span><span class="default">$this</span><span class="keyword">-></span><span class="default">setVar</span><span class="keyword">(</span><span class="string">'validpermission'</span><span class="keyword">, </span><span class="default">0</span><span class="keyword">);<br /> </span><span class="default">$this</span><span class="keyword">-></span><span class="default">setVar</span><span class="keyword">(</span><span class="string">'error'</span><span class="keyword">, </span><span class="string">'invalid token'</span><span class="keyword">);<br /> return </span><span class="default">false</span><span class="keyword">;<br /> }<br /> <br /> if(</span><span class="default">$this</span><span class="keyword">-></span><span class="default">validpermission </span><span class="keyword">!==</span><span class="default">1</span><span class="keyword">){<br /> echo </span><span class="string">'invalid Permissions to run this script'</span><span class="keyword">;<br /> return </span><span class="default">false</span><span class="keyword">; <br /> }else{<br /> return </span><span class="default">true</span><span class="keyword">;<br /> }<br /> }<br /> <br />}<br /><br /></span><span class="default">?><br /></span><br /><span class="default"><?php $userid </span><span class="keyword">= *** </span><span class="comment">//make it what ever id you like </span><span class="default">?><br /></span><form name="newform" action="index.php" method="post"><br /><input type="text" name="potentialeveilfield" value="" size 30 /><br /><input type="hidden" name="token" value="<span class="default"><?php </span><span class="keyword">echo </span><span class="default">maketoken</span><span class="keyword">(</span><span class="default">newform</span><span class="keyword">, </span><span class="default">$userid</span><span class="keyword">); </span><span class="comment">//$userid here could be user profile id </span><span class="default">?></span>" /><br /><input type="submit" /><br /></form><br /><br />Now when processing the form... check the value of your token<br /><br /><span class="default"><?php<br /><br /></span><span class="comment">//well you know the form name<br /></span><span class="keyword">if(!</span><span class="default">checktoken</span><span class="keyword">(</span><span class="default">$_POST</span><span class="keyword">[</span><span class="string">'token'</span><span class="keyword">], </span><span class="string">'newform'</span><span class="keyword">, </span><span class="default">$userid</span><span class="keyword">))<br />{ </span><span class="comment">//failed<br /></span><span class="keyword">exit(); </span><span class="comment">//or what ever termination and notification method best suits you.<br />//you could also design the class your way to get more accurate fail (error messages from the var) <br /></span><span class="keyword">}<br /><br /></span><span class="comment">//you can now continue with input data clean up (validation)<br /><br /></span><span class="default">?></span></span></code></div> </div> </div></div> <div class="foot"><a href="/manual/add-note.php?sect=security.variables&repo=en&redirect=https://www.php.net/manual/en/security.variables.php">＋<small>add a note</small></a></div> </section> </section> <aside class='layout-menu'> <ul class='parent-menu-list'> <li> <a href="security.php">Security</a> <ul class='child-menu-list'> <li class=""> <a href="security.intro.php" title="Introduction">Introduction</a> </li> <li class=""> <a href="security.general.php" title="General considerations">General considerations</a> </li> <li class=""> <a href="security.cgi-bin.php" title="Installed as CGI binary">Installed as 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