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 'quote' 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 ; 
// @ @ 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; 
} 
　} 
} 
}