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/* | |
* XSS filter | |
* | |
* This was built from numerous sources | |
* (thanks all, sorry I didn't track to credit you) | |
* | |
* It was tested against *most* exploits here: http://ha.ckers.org/xss.html | |
* WARNING: Some weren't tested!!! | |
* Those include the Actionscript and SSI samples, or any newer than Jan 2011 | |
* | |
* | |
* TO-DO: compare to SymphonyCMS filter: | |
* https://github.com/symphonycms/xssfilter/blob/master/extension.driver.php | |
* (Symphony's is probably faster than my hack) | |
*/ | |
function xss_clean($data) | |
{ | |
// Fix &entity\n; | |
$data = str_replace(array('&','<','>'), array('&amp;','&lt;','&gt;'), $data); | |
$data = preg_replace('/(&#*\w+)[\x00-\x20]+;/u', '$1;', $data); | |
$data = preg_replace('/(&#x*[0-9A-F]+);*/iu', '$1;', $data); | |
$data = html_entity_decode($data, ENT_COMPAT, 'UTF-8'); | |
// Remove any attribute starting with "on" or xmlns | |
$data = preg_replace('#(<[^>]+?[\x00-\x20"\'])(?:on|xmlns)[^>]*+>#iu', '$1>', $data); | |
// Remove javascript: and vbscript: protocols | |
$data = preg_replace('#([a-z]*)[\x00-\x20]*=[\x00-\x20]*([`\'"]*)[\x00-\x20]*j[\x00-\x20]*a[\x00-\x20]*v[\x00-\x20]*a[\x00-\x20]*s[\x00-\x20]*c[\x00-\x20]*r[\x00-\x20]*i[\x00-\x20]*p[\x00-\x20]*t[\x00-\x20]*:#iu', '$1=$2nojavascript...', $data); | |
$data = preg_replace('#([a-z]*)[\x00-\x20]*=([\'"]*)[\x00-\x20]*v[\x00-\x20]*b[\x00-\x20]*s[\x00-\x20]*c[\x00-\x20]*r[\x00-\x20]*i[\x00-\x20]*p[\x00-\x20]*t[\x00-\x20]*:#iu', '$1=$2novbscript...', $data); | |
$data = preg_replace('#([a-z]*)[\x00-\x20]*=([\'"]*)[\x00-\x20]*-moz-binding[\x00-\x20]*:#u', '$1=$2nomozbinding...', $data); | |
// Only works in IE: <span style="width: expression(alert('Ping!'));"></span> | |
$data = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?expression[\x00-\x20]*\([^>]*+>#i', '$1>', $data); | |
$data = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?behaviour[\x00-\x20]*\([^>]*+>#i', '$1>', $data); | |
$data = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?s[\x00-\x20]*c[\x00-\x20]*r[\x00-\x20]*i[\x00-\x20]*p[\x00-\x20]*t[\x00-\x20]*:*[^>]*+>#iu', '$1>', $data); | |
// Remove namespaced elements (we do not need them) | |
$data = preg_replace('#</*\w+:\w[^>]*+>#i', '', $data); | |
do | |
{ | |
// Remove really unwanted tags | |
$old_data = $data; | |
$data = preg_replace('#</*(?:applet|b(?:ase|gsound|link)|embed|frame(?:set)?|i(?:frame|layer)|l(?:ayer|ink)|meta|object|s(?:cript|tyle)|title|xml)[^>]*+>#i', '', $data); | |
} | |
while ($old_data !== $data); | |
// we are done... | |
return $data; | |
} |
Thanks man, help me alot
Thank for your effort
Does this also cover tags with uppercase text. I know that's not proper formatting for a tag, but what if someone is inserting data into their DB after turning it lowercase?
Thanks for your effort:)
Here is the bypass, I think:
<img src =x onerror=confirm(document.cookie);
The regular expression (https://gist.github.com/mbijon/1098477#file-xss_clean-php-L26) expects that attacker will use the closing angular bracket which is missing in the above vector and all browsers will render this ...
Thanks a lot my fellow developer
I think If you take a look at the anti xss library in the link
and compare it with yours you can improve your code even further
https://code.google.com/p/php-antixss/downloads/detail?name=AntiXSS.php&can=2&q=
thanks for a lot
helpful
@ALL -- FYI that I haven't updated this function since 2011 ...so that's likely one of MANY VULNS in this lib. Unless you have performance constraints I recommend HTML Purifier instead of this quick & dirty method.
It might be time to update or just pull this lib down.:
Tks
I tried to add to test DB xss_clean("< a href="#">a</ a>") (without spaces). It added and destroy some data. Is it bug? Or it's not XSS category?
thanks for a lot
helpful
A better alternative to this class https://github.com/ymakux/xss
Ready for production. Based on Kses and Drupal 7 filter
please I need a case that this filter can not catch i try most of cases but these cases were catches please and need at least one case that bypass this filter
rola2010 : test" onmouseover="alert(document.cookie);"
Asynth: unfortunately the code catch this,it seems it can't be broken
I still recommend HTML Purifier or kses instead of this gist.
However:
- UPDATED: This class-based version of xssClean recurses BOTH the encoded entity & tag removal routines. This solves a vulnerability found by 0xmitsurugi & reported privately.
- UPDATED: The exploit reported by @soaj1664 in this comment is fixed. It could have only been effective at the end of the file or if there were no other ">" characters after their exploit ...the problem with filtering that exploint without ONLY a closing ">" is that users would see removal of the entire input body. Instead of removing the entire message body after that exploit, I've chosen to remove up to the next non-word character (such as a newline or file ending char). This could still remove the rest of the input if there are no non-word characters before the end, but it helps keep some of the message in MOST cases, but still making this filter more secure.
👍
thank you so much
Hello, I am new to all xss stuff
how to prevent this
<?php
$_GET['a'] = 'javascript:alert(document.cookie)';
$href = xssClean($_GET['a']);
echo '<a href="'.$href.'">XSS link</a>';
?>
Just echo it with htmlspecialchars(). Example:
$_GET['a'] = 'javascript:alert(document.cookie)';
$href = $_GET['a'];
echo '<a href="'.htmlspecialchars($href).'">XSS link</a>';
?>
pice of code ;)
Hi,
I was testing your filter against a set of XSS test inputs. It seems that your filter is still vulnerable to XSS such as with inputs that contain XSS payloads in the comment-type, anchor and image tags. Examples of one of each are:
<!--#exec cmd=""/usr/X11R6/bin/xterm ?display 127.0.0.1:0 &""-->
<a href="jAvAsCrIpT:alert(1)">X</a>
/><img/onerror=\x09javascript:alert(1)\x09src=xxx:x />
A full report can be read in our paper, "Assessment of Dynamic Open-source Cross-site Scripting Filters as Security Devices in Web Applications". I kindly suggest that you add these tags to the blacklist to make it more robust against XSS.
Thank you.
@nat4tq share your paper with us then :)
@nat4tq I tried the code you provided on the local server. This is really a problem. Do you have any solutions?
@nat4tq I tried the code you provided on the local server. This is really a problem. Do you have any solutions?
You could try this library : https://github.com/voku/anti-xss
My method is deprecated. I now recommend http://htmlpurifier.org/
Thanks for it man! it helped :)