XSS Filter

Auteur: Kallahar.com - 27 mei 2009 - 17:04 - Gekeurd door: Gerard - Hits: 4687 - Aantal punten: (0 stemmen)

Deze functie is uitermate handig voor het wegfilteren onveilige inhoud bij het verwerken/weergeven van gegevens. Met deze functie worden XSS aanvallen dus volledig onschadelijk gemaakt.

Van: http://kallahar...nction.php

Voorbeeld onderaan!

Noot: Een misschien nog betere filter is HTML Purifier.

Code:

php code - Bekijk de code zonder highlighting - Klap code in

<?php
function RemoveXSS($val) 
{
	// remove all non-printable characters. CR(0a) and LF(0b) and TAB(9) are allowed
	// this prevents some character re-spacing such as <java\0script>
	// note that you have to handle splits with \n, \r, and \t later since they *are* allowed in some inputs
	$val = preg_replace('/([\x00-\x08,\x0b-\x0c,\x0e-\x19])/', '', $val);
	
	// straight replacements, the user should never need these since they're normal characters
	// this prevents like <IMG SRC=&#X40&#X61&#X76&#X61&#X73&#X63&#X72&#X69&#X70&#X74&#X3A &#X61&#X6C&#X65&#X72&#X74&#X28&#X27&#X58&#X53&#X53&#X27&#X29>
	$search = '[a-zA-Z0-9]';
	$search .= '!@#$%^&*()';
	$search .= '~`";:?+/={}[]-\\_|\'';
	for ($i = 0; $i < strlen($search); $i++) 
	{
		// ;? matches the ;, which is optional
		// 0{0,7} matches any padded zeros, which are optional and go up to 8 chars
		
		// &#x0040 @ search for the hex values
		$val = preg_replace('/(&#[xX]0{0,8}'.dechex(ord($search[$i])).';?)/i', $search[$i], $val); // with a ;
		// &#00064 @ 0{0,7} matches '0' zero to seven times
		$val = preg_replace('/(&#0{0,8}'.ord($search[$i]).';?)/', $search[$i], $val); // with a ;
	}
	
	// now the only remaining whitespace attacks are \t, \n, and \r
	$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);
	
	$found = true; // keep replacing as long as the previous round replaced something
	while ($found) 
	{
		$val_before = $val;
		for ($i = 0; $i < sizeof($ra); $i++) 
		{
			$pattern = '/';
			for ($j = 0; $j < strlen($ra[$i]); $j++) 
			{
				if ($j > 0) 
				{
					$pattern .= '(';
					$pattern .= '(&#[xX]0{0,8}([9ab]);)';
					$pattern .= '|';
					$pattern .= '|(&#0{0,8}([9|10|13]);)';
					$pattern .= ')*';
				}
				$pattern .= $ra[$i][$j];
			}
			$pattern .= '/i';
			$replacement = substr($ra[$i], 0, 2).'<x>'.substr($ra[$i], 2); // add in <> to nerf the tag
			$val = preg_replace($pattern, $replacement, $val); // filter out the hex tags
			if ($val_before == $val) 
			{
				// no replacements were made, so exit the loop
				$found = false;
			}
		}
	}
	return $val;
} 
?>

<?php
function RemoveXSS($val) 
{
	// remove all non-printable characters. CR(0a) and LF(0b) and TAB(9) are allowed
	// this prevents some character re-spacing such as <java\0script>
	// note that you have to handle splits with \n, \r, and \t later since they *are* allowed in some inputs
	$val = preg_replace('/([\x00-\x08,\x0b-\x0c,\x0e-\x19])/', '', $val);
 
	// straight replacements, the user should never need these since they're normal characters
	// this prevents like <IMG SRC=&#X40&#X61&#X76&#X61&#X73&#X63&#X72&#X69&#X70&#X74&#X3A &#X61&#X6C&#X65&#X72&#X74&#X28&#X27&#X58&#X53&#X53&#X27&#X29>
	$search = '[a-zA-Z0-9]';
	$search .= '!@#$%^&*()';
	$search .= '~`";:?+/={}[]-\\_|\'';
	for ($i = 0; $i < strlen($search); $i++) 
	{
		// ;? matches the ;, which is optional
		// 0{0,7} matches any padded zeros, which are optional and go up to 8 chars
 
		// &#x0040 @ search for the hex values
		$val = preg_replace('/(&#[xX]0{0,8}'.dechex(ord($search[$i])).';?)/i', $search[$i], $val); // with a ;
		// &#00064 @ 0{0,7} matches '0' zero to seven times
		$val = preg_replace('/(&#0{0,8}'.ord($search[$i]).';?)/', $search[$i], $val); // with a ;
	}
 
	// now the only remaining whitespace attacks are \t, \n, and \r
	$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);
 
	$found = true; // keep replacing as long as the previous round replaced something
	while ($found) 
	{
		$val_before = $val;
		for ($i = 0; $i < sizeof($ra); $i++) 
		{
			$pattern = '/';
			for ($j = 0; $j < strlen($ra[$i]); $j++) 
			{
				if ($j > 0) 
				{
					$pattern .= '(';
					$pattern .= '(&#[xX]0{0,8}([9ab]);)';
					$pattern .= '|';
					$pattern .= '|(&#0{0,8}([9|10|13]);)';
					$pattern .= ')*';
				}
				$pattern .= $ra[$i][$j];
			}
			$pattern .= '/i';
			$replacement = substr($ra[$i], 0, 2).'<x>'.substr($ra[$i], 2); // add in <> to nerf the tag
			$val = preg_replace($pattern, $replacement, $val); // filter out the hex tags
			if ($val_before == $val) 
			{
				// no replacements were made, so exit the loop
				$found = false;
			}
		}
	}
	return $val;
} 
?>

Voorbeeld:

php code - Bekijk de code zonder highlighting - Klap code in

echo RemoveXSS('<script>alert(/xss injection/);</script>');
echo '<br />';
echo RemoveXSS('<SCRIPT>alert(String.fromCharCode(88,83,83))</SCRIPT>');
/* geeft:
ript>alert(/xss injection/);ript>
ript>alert(String.fromCharCode(888383))ript> */

echo RemoveXSS('<script>alert(/xss injection/);</script>');
echo '<br />';
echo RemoveXSS('<SCRIPT>alert(String.fromCharCode(88,83,83))</SCRIPT>');
/* geeft:
ript>alert(/xss injection/);ript>
ript>alert(String.fromCharCode(888383))ript> */

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