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';
　$search .= '[email protected]#$%^&*()';
　$search .= '~`";:?+/={}[]-_|/'//';
　for ($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;
　　}
　}
}
}