Reputation: 10124
Does anyone know of a good function out there for filtering generic input from forms? Zend_Filter_input seems to require prior knowledge of the contents of the input and I'm concerned that using something like HTML Purifier will have a big performance impact.
What about something like:
function sacarXss($val) {
$val = preg_replace('/([\x00-\x08][\x0b-\x0c][\x0e-\x20])/', '', $val);
$search = 'abcdefghijklmnopqrstuvwxyz';
$search .= 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
$search .= '1234567890!@#$%^&*()';
$search .= '~`";:?+/={}[]-_|\'\\';
for ($i = 0; $i < strlen($search); $i++) {
$val = preg_replace('/(&#[x|X]0{0,8}'.dechex(ord($search[$i])).';?)/i', $search[$i], $val); // with a ;
$val = preg_replace('/(�{0,8}'.ord($search[$i]).';?)/', $search[$i], $val); // with a ;
}
$ra1 = Array('javascript', 'vbscript', 'expression', 'applet', 'meta', 'xml', 'blink', 'link', 'style', 'script', 'embed', 'object', 'iframe', 'frame', 'frameset', 'ilayer', 'layer', 'bgsound', 'title', 'base');
$ra2 = Array('onabort', 'onactivate', 'onafterprint', 'onafterupdate', 'onbeforeactivate', 'onbeforecopy', 'onbeforecut', 'onbeforedeactivate', 'onbeforeeditfocus', 'onbeforepaste', 'onbeforeprint', 'onbeforeunload', 'onbeforeupdate', 'onblur', 'onbounce', 'oncellchange', 'onchange', 'onclick', 'oncontextmenu', 'oncontrolselect', 'oncopy', 'oncut', 'ondataavailable', 'ondatasetchanged', 'ondatasetcomplete', 'ondblclick', 'ondeactivate', 'ondrag', 'ondragend', 'ondragenter', 'ondragleave', 'ondragover', 'ondragstart', 'ondrop', 'onerror', 'onerrorupdate', 'onfilterchange', 'onfinish', 'onfocus', 'onfocusin', 'onfocusout', 'onhelp', 'onkeydown', 'onkeypress', 'onkeyup', 'onlayoutcomplete', 'onload', 'onlosecapture', 'onmousedown', 'onmouseenter', 'onmouseleave', 'onmousemove', 'onmouseout', 'onmouseover', 'onmouseup', 'onmousewheel', 'onmove', 'onmoveend', 'onmovestart', 'onpaste', 'onpropertychange', 'onreadystatechange', 'onreset', 'onresize', 'onresizeend', 'onresizestart', 'onrowenter', 'onrowexit', 'onrowsdelete', 'onrowsinserted', 'onscroll', 'onselect', 'onselectionchange', 'onselectstart', 'onstart', 'onstop', 'onsubmit', 'onunload');
$ra = array_merge($ra1, $ra2);
$found = true;
while ($found == true) {
$val_before = $val;
for ($i = 0; $i < sizeof($ra); $i++) {
$pattern = '/';
for ($j = 0; $j < strlen($ra[$i]); $j++) {
if ($j > 0) {
$pattern .= '(';
$pattern .= '(&#[x|X]0{0,8}([9][a][b]);?)?';
$pattern .= '|(�{0,8}([9][10][13]);?)?';
$pattern .= ')?';
}
$pattern .= $ra[$i][$j];
}
$pattern .= '/i';
$replacement = substr($ra[$i], 0, 2).'<x>'.substr($ra[$i], 2);
$val = preg_replace($pattern, $replacement, $val);
if ($val_before == $val) {
$found = false;
}
}
}
return $val;
}
echo sacarXss("testeando javascript:alert('hola');");
Upvotes: 47
Views: 123623
Reputation:
I'm was collect most of issues by the web and combine stepping filter for all of them.
After some testing seems it works perfect:
/*
* Total XSS preventer class by Full-R
*
*/
final class xCleaner {
public static function clean( string $html ): string {
return self::cleanXSS(
preg_replace(
[
'/\s?<iframe[^>]*?>.*?<\/iframe>\s?/si',
'/\s?<style[^>]*?>.*?<\/style>\s?/si',
'/\s?<script[^>]*?>.*?<\/script>\s?/si',
'#\son\w*="[^"]+"#',
],
[
'',
'',
''
],
$html
)
);
}
protected static function hexToSymbols( string $s ): string {
return html_entity_decode($s, ENT_XML1, 'UTF-8');
}
protected static function escape( string $s, string $m = 'attr' ): string {
preg_match_all('/data:\w+\/([a-zA-Z]*);base64,(?!_#_#_)([^)\'"]*)/mi', $s, $b64, PREG_OFFSET_CAPTURE);
if( count( array_filter( $b64 ) ) > 0 ) {
switch( $m ) {
case 'attr':
$xclean = self::cleanXSS(
urldecode(
base64_decode(
$b64[ 2 ][ 0 ][ 0 ]
)
)
);
break;
case 'tag':
$xclean = self::cleanTagInnerXSS(
urldecode(
base64_decode(
$b64[ 2 ][ 0 ][ 0 ]
)
)
);
break;
}
return substr_replace(
$s,
'_#_#_'. base64_encode( $xclean ),
$b64[ 2 ][ 0 ][ 1 ],
strlen( $b64[ 2 ][ 0 ][ 0 ] )
);
}
else {
return $s;
}
}
protected static function cleanXSS( string $s ): string {
// base64 injection prevention
$st = self::escape( $s, 'attr' );
return preg_replace([
// JSON unicode
'/\\\\u?{?([a-f0-9]{4,}?)}?/mi', // [1] unicode JSON clean
// Data b64 safe
'/\*\w*\*/mi', // [2] unicode simple clean
// Malware payloads
'/:?e[\s]*x[\s]*p[\s]*r[\s]*e[\s]*s[\s]*s[\s]*i[\s]*o[\s]*n[\s]*(:|;|,)?\w*/mi', // [3] (:expression) evalution
'/l[\s]*i[\s]*v[\s]*e[\s]*s[\s]*c[\s]*r[\s]*i[\s]*p[\s]*t[\s]*(:|;|,)?\w*/mi', // [4] (livescript:) evalution
'/j[\s]*s[\s]*c[\s]*r[\s]*i[\s]*p[\s]*t[\s]*(:|;|,)?\w*/mi', // [5] (jscript:) evalution
'/j[\s]*a[\s]*v[\s]*a[\s]*s[\s]*c[\s]*r[\s]*i[\s]*p[\s]*t[\s]*(:|;|,)?\w*/mi', // [6] (javascript:) evalution
'/b[\s]*e[\s]*h[\s]*a[\s]*v[\s]*i[\s]*o[\s]*r[\s]*(:|;|,)?\w*/mi', // [7] (behavior:) evalution
'/v[\s]*b[\s]*s[\s]*c[\s]*r[\s]*i[\s]*p[\s]*t[\s]*(:|;|,)?\w*/mi', // [8] (vsbscript:) evalution
'/v[\s]*b[\s]*s[\s]*(:|;|,)?\w*/mi', // [9] (vbs:) evalution
'/e[\s]*c[\s]*m[\s]*a[\s]*s[\s]*c[\s]*r[\s]*i[\s]*p[\s]*t*(:|;|,)?\w*/mi', // [10] (ecmascript:) possible ES evalution
'/b[\s]*i[\s]*n[\s]*d[\s]*i[\s]*n[\s]*g*(:|;|,)?\w*/mi', // [11] (-binding) payload
'/\+\/v(8|9|\+|\/)?/mi', // [12] (UTF-7 mutation)
// Some entities
'/&{\w*}\w*/mi', // [13] html entites clenup
'/&#\d+;?/m', // [14] html entites clenup
// Script tag encoding mutation issue
'/\¼\/?\w*\¾\w*/mi', // [21] mutation KOI-8
'/\+ADw-\/?\w*\+AD4-\w*/mi', // [22] mutation old encodings
'/\/*?%00*?\//m',
// base64 escaped
'/_#_#_/mi', // [23] base64 escaped marker cleanup
],
// Replacements steps :: 23
['&#x$1;', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', '', ''],
str_ireplace(
['\u0', ':', '&tab;', '&newline;'],
['\0', ':', '', ''],
// U-HEX prepare step
self::hexToSymbols( $st ))
);
}
}
Also you can add Tidy markup correction to make HTML valid.
Upvotes: 0
Reputation: 1
I found a solution for my problem with the posts with german umlaut. To provide from totally cleaning (killing) the posts, i encode the incoming data:
*$data = utf8_encode($data);
... function ...*
And at last i decode the output to get correct signs:
*$data = utf8_decode($data);*
Now the post go through the filter function and i get a correct result...
Upvotes: -1
Reputation: 3495
All above methods don't allow to preserve some tags like <a>
, <table>
etc. There is an ultimate solution http://sourceforge.net/projects/kses/
Drupal uses it
Upvotes: 0
Reputation: 4383
htmlspecialchars()
is perfectly adequate for filtering user input that is displayed in html forms.
Upvotes: 1
Reputation: 1
Try using for Clean XSS
xss_clean($data): "><script>alert(String.fromCharCode(74,111,104,116,111,32,82,111,98,98,105,101))</script>
Upvotes: -2
Reputation: 625485
Simple way? Use strip_tags()
:
$str = strip_tags($input);
You can also use filter_var()
for that:
$str = filter_var($input, FILTER_SANITIZE_STRING);
The advantage of filter_var()
is that you can control the behaviour by, for example, stripping or encoding low and high characters.
Here is a list of sanitizing filters.
Upvotes: 87
Reputation: 171
I have a similar problem. I need users to submit html content to a profile page with a great WYSIWYG editor (Redactorjs!), i wrote the following function to clean the submitted html:
<?php function filterxss($str) {
//Initialize DOM:
$dom = new DOMDocument();
//Load content and add UTF8 hint:
$dom->loadHTML('<meta http-equiv="content-type" content="text/html; charset=utf-8">'.$str);
//Array holds allowed attributes and validation rules:
$check = array('src'=>'#(http://[^\s]+(?=\.(jpe?g|png|gif)))#i','href'=>'|^http(s)?://[a-z0-9-]+(.[a-z0-9-]+)*(:[0-9]+)?(/.*)?$|i');
//Loop all elements:
foreach($dom->getElementsByTagName('*') as $node){
for($i = $node->attributes->length -1; $i >= 0; $i--){
//Get the attribute:
$attribute = $node->attributes->item($i);
//Check if attribute is allowed:
if( in_array($attribute->name,array_keys($check))) {
//Validate by regex:
if(!preg_match($check[$attribute->name],$attribute->value)) {
//No match? Remove the attribute
$node->removeAttributeNode($attribute);
}
}else{
//Not allowed? Remove the attribute:
$node->removeAttributeNode($attribute);
}
}
}
var_dump($dom->saveHTML()); } ?>
The $check array holds all the allowed attributes and validation rules. Maybe this is useful for some of you. I haven't tested is yet, so tips are welcome
Upvotes: 3
Reputation: 582
According to www.mcafeesecure.com General Solution for vulnerable to cross-site scripting (XSS) filter function can be:
function xss_cleaner($input_str) {
$return_str = str_replace( array('<','>',"'",'"',')','('), array('<','>',''','"',')','('), $input_str );
$return_str = str_ireplace( '%3Cscript', '', $return_str );
return $return_str;
}
Upvotes: 0
Reputation: 29
function clean($data){
$data = rawurldecode($data);
return filter_var($data, FILTER_SANITIZE_SPEC_CHARS);
}
Upvotes: 2
Reputation: 382919
There are a number of ways hackers put to use for XSS attacks, PHP's built-in functions do not respond to all sorts of XSS attacks. Hence, functions such as strip_tags, filter_var, mysql_real_escape_string, htmlentities, htmlspecialchars, etc do not protect us 100%. You need a better mechanism, here is what is solution:
function xss_clean($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;
}
Upvotes: 33