如何利用php防止XSS跨站脚本攻击

<?php

$str = "A "quote" is ＜b＞bold＜/b＞";

// Outputs: A "quote" is bold

echo htmlentities($str);

// Outputs: A "quote" is bold

echo htmlentities($str, ENT_QUOTES);

?>

这样可以使非法的脚本失效。

但是要注意一点，htmlentities()默认编码为 ISO-8859-1，如果你的非法脚本编码为其它，那么可能无法过滤掉，同时浏览器却可以识别和执行。这个问题我先找几个站点测试后再说。

以下是一个过滤非法脚本的函数,仅供参考：

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 <javascript>

// note that you have to handle splits with , , and 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=@avascript:a&

_#X6Cert('XSS')>

$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

// @ @ 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

$val = preg_replace("/(�{0,8}".ord($search[$i]).";?)/", $search[$i], $val); // with a ;

}

// now the only remaining whitespace attacks are , , and

$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}([a][b]);?)?";

$pattern .= "|(�{0,8}([10][13]);?)?";

$pattern .= ")?";

}

$pattern .= $ra[$i][$j];

} www.2cto.com

$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;

}

}

}

}