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如果你不懂什么是XSS，可以看這里，或者這里（中文的也許會(huì)好懂一些）。
國(guó)內(nèi)不少論壇都存在跨站腳本漏洞，例如這里 有一個(gè)Google Hack+XSS的攻擊例子，針對(duì)的是Discuz 4.0.0RC3。國(guó)外也很多這樣的例子，甚至Google也出現(xiàn)過(guò)，不過(guò)在12月初時(shí)修正了。跨站攻擊很容易就可以構(gòu)造，而且非常隱蔽，不易被查覺(jué)（通常盜取信息后馬上跳轉(zhuǎn)回原頁(yè)面）。
如何攻擊，在此不作說(shuō)明（也不要問(wèn)我），主要談?wù)勅绾畏婪丁Ｊ紫龋缯灸_本攻擊都是由于對(duì)用戶的輸入沒(méi)有進(jìn)行嚴(yán)格的過(guò)濾造成的，所以我們必須在所有數(shù)據(jù)進(jìn)入我們的網(wǎng)站和數(shù)據(jù)庫(kù)之前把可能的危險(xiǎn)攔截。針對(duì)非法的HTML代碼包括單雙引號(hào)等，可以使用htmlentities() 。
<?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($str, ENT_QUOTES);
?>
這樣可以使非法的腳本失效。
但是要注意一點(diǎn)，htmlentities()默認(rèn)編碼為 ISO-8859-1，如果你的非法腳本編碼為其它，那么可能無(wú)法過(guò)濾掉，同時(shí)瀏覽器卻可以識(shí)別和執(zhí)行。這個(gè)問(wèn)題我先找?guī)讉€(gè)站點(diǎn)測(cè)試后再說(shuō)。
這里提供一個(gè)過(guò)濾非法腳本的函數(shù)：
function RemoveXSS($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=@avascript:alert('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 /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 .= '|(�{0,8}([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;
}
}
}
}
php技術(shù)：PHP和XSS跨站攻擊的防范，轉(zhuǎn)載需保留來(lái)源！
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