利用PHP编程防范XSS跨站脚本攻击

<?php
$str = "A 'quote' is <b>bold</b>";

// Outputs: A 'quote' is <b>bold</b>
echo htmlentities($str);

// Outputs: A &#039;quote&#039; is <b>bold</b>
echo htmlentities($str, ENT_QUOTES);
?>

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-\x20])/', '', $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 = 'abcdefghijklmnopqrstuvwxyz'; 
	$search .= 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'; 
	$search .= '1234567890!@#$%^&*()'; 
	$search .= ''`";:?+/={}[]-_|\'\\'; 
	for ($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 
		$val = preg_replace('/(&#[x|X]0{0,8}'.dechex(ord($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 == 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{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; 
			} 
		} 
	} 
}