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<?php | |
/* | |
* XSS filter, recursively handles HTML tags & UTF encoding | |
* Optionally handles base64 encoding | |
* | |
* ***DEPRECATION RECOMMENDED*** Not updated or maintained since 2011 | |
* A MAINTAINED & BETTER ALTERNATIVE => kses | |
* https://github.com/RichardVasquez/kses/ | |
* | |
* 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 | |
* | |
*/ | |
class xssClean { | |
/* | |
* Recursive worker to strip risky elements | |
* | |
* @param string $input Content to be cleaned. It MAY be modified in output | |
* @return string $output Modified $input string | |
*/ | |
public function clean_input( $input, $safe_level = 0 ) { | |
$output = $input; | |
do { | |
// Treat $input as buffer on each loop, faster than new var | |
$input = $output; | |
// Remove unwanted tags | |
$output = $this->strip_tags( $input ); | |
$output = $this->strip_encoded_entities( $output ); | |
// Use 2nd input param if not empty or '0' | |
if ( $safe_level !== 0 ) { | |
$output = $this->strip_base64( $output ); | |
} | |
} while ( $output !== $input ); | |
return $output; | |
} | |
/* | |
* Focuses on stripping encoded entities | |
* *** This appears to be why people use this sample code. Unclear how well Kses does this *** | |
* | |
* @param string $input Content to be cleaned. It MAY be modified in output | |
* @return string $input Modified $input string | |
*/ | |
private function strip_encoded_entities( $input ) { | |
// Fix &entity\n; | |
$input = str_replace(array('&','<','>'), array('&amp;','&lt;','&gt;'), $input); | |
$input = preg_replace('/(&#*\w+)[\x00-\x20]+;/u', '$1;', $input); | |
$input = preg_replace('/(&#x*[0-9A-F]+);*/iu', '$1;', $input); | |
$input = html_entity_decode($input, ENT_COMPAT, 'UTF-8'); | |
// Remove any attribute starting with "on" or xmlns | |
$input = preg_replace('#(<[^>]+?[\x00-\x20"\'])(?:on|xmlns)[^>]*+[>\b]?#iu', '$1>', $input); | |
// Remove javascript: and vbscript: protocols | |
$input = 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...', $input); | |
$input = 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...', $input); | |
$input = preg_replace('#([a-z]*)[\x00-\x20]*=([\'"]*)[\x00-\x20]*-moz-binding[\x00-\x20]*:#u', '$1=$2nomozbinding...', $input); | |
// Only works in IE: <span style="width: expression(alert('Ping!'));"></span> | |
$input = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?expression[\x00-\x20]*\([^>]*+>#i', '$1>', $input); | |
$input = preg_replace('#(<[^>]+?)style[\x00-\x20]*=[\x00-\x20]*[`\'"]*.*?behaviour[\x00-\x20]*\([^>]*+>#i', '$1>', $input); | |
$input = 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>', $input); | |
return $input; | |
} | |
/* | |
* Focuses on stripping unencoded HTML tags & namespaces | |
* | |
* @param string $input Content to be cleaned. It MAY be modified in output | |
* @return string $input Modified $input string | |
*/ | |
private function strip_tags( $input ) { | |
// Remove tags | |
$input = preg_replace('#</*(?:applet|b(?:ase|gsound|link)|embed|frame(?:set)?|i(?:frame|layer)|l(?:ayer|ink)|meta|object|s(?:cript|tyle)|title|xml)[^>]*+>#i', '', $input); | |
// Remove namespaced elements | |
$input = preg_replace('#</*\w+:\w[^>]*+>#i', '', $input); | |
return $input; | |
} | |
/* | |
* Focuses on stripping entities from Base64 encoded strings | |
* | |
* NOT ENABLED by default! | |
* To enable 2nd param of clean_input() can be set to anything other than 0 or '0': | |
* ie: xssClean->clean_input( $input_string, 1 ) | |
* | |
* @param string $input Maybe Base64 encoded string | |
* @return string $output Modified & re-encoded $input string | |
*/ | |
private function strip_base64( $input ) { | |
$decoded = base64_decode( $input ); | |
$decoded = $this->strip_tags( $decoded ); | |
$decoded = $this->strip_encoded_entities( $decoded ); | |
$output = base64_encode( $decoded ); | |
return $output; | |
} | |
} |
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/
Hello, I am new to all xss stuff
how to prevent this