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?和記娛h188下載app:利用PHP編程防范XSS跨站腳本攻擊

?

海內不少論壇都存在跨站腳本破綻,國外也很多這樣的例子,以致Google也呈現過,不過在12月初時修正了。(編者注:關于跨站腳本破綻進擊,讀者可參閱《詳解XSS跨站腳本進擊》)??缯具M擊很輕易就可以構造,而且異常隱蔽,不易被查覺(平日竊守信息后頓時跳轉回原頁面)。

若何進擊,在此不作闡明(也不要問我),主要談談若何警備。首先,跨站腳本進擊都是因為對用戶的輸入沒有進行嚴格的過濾造成的,以是我們必須在所稀有據進入我們的網站和數據庫之前把可能的危險攔截。針對不法的HTML代碼包括單雙引號等,可以應用htmlentities() 。

<?php

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

// Outputs: A 'quote' is <b>bold&l?和記娛h188下載appt;/b>

echo htmlentities($str);

// Outputs: A 'quote' is <b>bold</b>

echo htmlentities($str, ENT_QUOTES);

?>

這樣可以使不法的腳本掉效。

然則要留意一點,htmlentities()默認編碼為 ISO-8859-1,假如你的不法腳本編碼為其它,那么可能無法過濾掉落,同時瀏覽器卻可以識別和履行。這個問題我先找幾個站點測試后再說。

這里供給一個過濾不法腳本的函數:

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';

$search .= '12345678?和記娛h188下載[email protected]#$%^&*()';

$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

// @ @ 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', 'on?和記娛h188下載appdragenter', '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'?和記娛h188下載app, '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 somet?和記娛h188下載apphing

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;

}

}

}

}

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