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<?php
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/**
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* This file is part of the O2System Framework package.
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*
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* For the full copyright and license information, please view the LICENSE
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* file that was distributed with this source code.
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*
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* @author Steeve Andrian Salim
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* @copyright Copyright (c) Steeve Andrian Salim
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*/
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// ------------------------------------------------------------------------
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namespace O2System\Security\Filters;
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/**
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* Class Xss
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*
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* @package O2System\Security\Filters
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*/
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class Xss
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{
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/**
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* Clean
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*
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* @param string $string
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* @param boolean $isImage
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*
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* @return string
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*/
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public static function clean($string, $isImage = false)
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{
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// Is the string an array?
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if (is_array($string)) {
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while (list($key) = each($string)) {
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$string[ $key ] = self::clean($string[ $key ]);
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}
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return $string;
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}
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// Remove Invisible Characters
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$string = remove_invisible_characters($string);
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/*
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* URL Decode
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*
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* Just in case stuff like this is submitted:
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*
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* <a href="http://%77%77%77%2E%67%6F%6F%67%6C%65%2E%63%6F%6D">Google</a>
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*
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* Note: Use rawurldecode() so it does not remove plus signs
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*/
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do {
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$string = rawurldecode($string);
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} while (preg_match('/%[0-9a-f]{2,}/i', $string));
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/*
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* Convert character entities to ASCII
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*
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* This permits our tests below to work reliably.
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* We only convert entities that are within tags since
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* these are the ones that will pose security problems.
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*/
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$string = preg_replace_callback(
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"/[^a-z0-9>]+[a-z0-9]+=([\'\"]).*?\\1/si",
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[self::class, 'convertAttribute'],
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$string
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);
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$string = preg_replace_callback('/<\w+.*/si', [self::class, 'decodeEntity'], $string);
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// Remove Invisible Characters Again!
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$string = remove_invisible_characters($string);
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/*
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* Convert all tabs to spaces
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*
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* This prevents strings like this: ja vascript
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* NOTE: we deal with spaces between characters later.
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* NOTE: preg_replace was found to be amazingly slow here on
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* large blocks of data, so we use str_replace.
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*/
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$string = str_replace("\t", ' ', $string);
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// Capture converted string for later comparison
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$convertedString = $string;
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// Remove Strings that are never allowed
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$string = self::doNeverAllowed($string);
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/*
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* Makes PHP tags safe
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*
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* Note: XML tags are inadvertently replaced too:
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*
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* <?xml
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*
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* But it doesn't seem to pose a problem.
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*/
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if ($isImage === true) {
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// Images have a tendency to have the PHP short opening and
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// closing tags every so often so we skip those and only
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// do the long opening tags.
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$string = preg_replace('/<\?(php)/i', '<?\\1', $string);
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} else {
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$string = str_replace(['<?', '?' . '>'], ['<?', '?>'], $string);
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}
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/*
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* Compact any exploded words
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*
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* This corrects words like: j a v a s c r i p t
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* These words are compacted back to their correct state.
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*/
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$words = [
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'javascript',
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'expression',
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'vbscript',
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'jscript',
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'wscript',
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'vbs',
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'script',
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'base64',
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'applet',
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'alert',
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'document',
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'write',
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'cookie',
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'window',
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'confirm',
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'prompt',
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'eval',
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];
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foreach ($words as $word) {
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$word = implode('\s*', str_split($word)) . '\s*';
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// We only want to do this when it is followed by a non-word character
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// That way valid stuff like "dealer to" does not become "dealerto"
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$string = preg_replace_callback(
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'#(' . substr($word, 0, -3) . ')(\W)#is',
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[self::class, 'compactExplodedWords'],
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$string
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);
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}
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/*
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* Remove disallowed Javascript in links or img tags
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* We used to do some version comparisons and use of stripos(),
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* but it is dog slow compared to these simplified non-capturing
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* preg_match(), especially if the pattern exists in the string
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*
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* Note: It was reported that not only space characters, but all in
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* the following pattern can be parsed as separators between a tag name
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* and its attributes: [\d\s"\'`;,\/\=\(\x00\x0B\x09\x0C]
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* ... however, remove_invisible_characters() above already strips the
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* hex-encoded ones, so we'll skip them below.
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*/
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do {
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$original = $string;
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if (preg_match('/<a/i', $string)) {
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$string = preg_replace_callback(
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'#<a[^a-z0-9>]+([^>]*?)(?:>|$)#si',
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[self::class, 'jsLinkRemoval'],
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$string
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);
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}
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if (preg_match('/<img/i', $string)) {
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$string = preg_replace_callback(
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'#<img[^a-z0-9]+([^>]*?)(?:\s?/?>|$)#si',
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[self::class, 'jsImgRemoval'],
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$string
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);
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}
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if (preg_match('/script|xss/i', $string)) {
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$string = preg_replace('#</*(?:script|xss).*?>#si', '[removed]', $string);
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}
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} while ($original !== $string);
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unset($original);
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/*
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* Sanitize naughty HTML elements
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*
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* If a tag containing any of the words in the list
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* below is found, the tag gets converted to entities.
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*
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* So this: <blink>
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* Becomes: <blink>
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*/
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$pattern = '#'
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. '<((?<slash>/*\s*)(?<tagName>[a-z0-9]+)(?=[^a-z0-9]|$)'
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// tag start and name, followed by a non-tag character
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. '[^\s\042\047a-z0-9>/=]*'
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// a valid attribute character immediately after the tag would count as a separator
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// optional attributes
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. '(?<attributes>(?:[\s\042\047/=]*'
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// non-attribute characters, excluding > (tag close) for obvious reasons
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. '[^\s\042\047>/=]+'
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// attribute characters
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// optional attribute-value
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. '(?:\s*='
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// attribute-value separator
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. '(?:[^\s\042\047=><`]+|\s*\042[^\042]*\042|\s*\047[^\047]*\047|\s*(?U:[^\s\042\047=><`]*))'
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// single, double or non-quoted value
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. ')?'
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// end optional attribute-value group
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. ')*)'
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// end optional attributes group
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. '[^>]*)(?<closeTag>\>)?#isS';
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// Note: It would be nice to optimize this for speed, BUT
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// only matching the naughty elements here results in
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// false positives and in turn - vulnerabilities!
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do {
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$oldString = $string;
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$string = preg_replace_callback($pattern, [self::class, 'sanitizeNaughtyHTML'], $string);
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} while ($oldString !== $string);
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unset($oldString);
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/*
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* Sanitize naughty scripting elements
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*
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* Similar to above, only instead of looking for
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* tags it looks for PHP and JavaScript commands
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* that are disallowed. Rather than removing the
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* code, it simply converts the parenthesis to entities
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* rendering the code un-executable.
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*
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* For example: eval('some code')
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* Becomes: eval('some code')
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*/
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$string = preg_replace(
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'#(alert|prompt|confirm|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si',
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'\\1\\2(\\3)',
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$string
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);
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// Final clean up
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// This adds a bit of extra precaution in case
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// something got through the above filters
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$string = self::doNeverAllowed($string);
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/*
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* Images are Handled in a Special Way
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* - Essentially, we want to know that after all of the character
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* conversion is done whether any unwanted, likely XSS, code was found.
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* If not, we return TRUE, as the image is clean.
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* However, if the string post-conversion does not matched the
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* string post-removal of XSS, then it fails, as there was unwanted XSS
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* code found and removed/changed during processing.
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*/
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if ($isImage === true) {
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return ($string === $convertedString);
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}
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return $string;
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}
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/**
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* Do Never Allowed
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*
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* @used-by XSS::clean()
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*
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* @param string
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*
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* @return string
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*/
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protected static function doNeverAllowed($string)
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{
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$string = str_replace(
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array_keys(self::getConfig('never_allowed_strings')),
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self::getConfig('never_allowed_strings'),
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$string
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);
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277
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foreach (self::getConfig('never_allowed_regex') as $regex) {
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$string = preg_replace('#' . $regex . '#is', '[removed]', $string);
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}
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return $string;
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}
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284
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// --------------------------------------------------------------------------------------
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285
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protected function getConfig($index)
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287
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{
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static $config;
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289
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290
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if (empty($config)) {
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$config = require('../Config/Xss.php');
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}
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return $config[ $index ];
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}
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297
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// --------------------------------------------------------------------
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298
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/**
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300
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* Compact Exploded Words
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301
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*
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302
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* Callback method for xss_clean() to remove whitespace from
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303
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|
|
* things like 'j a v a s c r i p t'.
|
|
304
|
|
|
*
|
|
305
|
|
|
* @used-by XSS::clean()
|
|
306
|
|
|
*
|
|
307
|
|
|
* @param array $matches
|
|
308
|
|
|
*
|
|
309
|
|
|
* @return string
|
|
310
|
|
|
*/
|
|
311
|
|
|
protected static function compactExplodedWords($matches)
|
|
312
|
|
|
{
|
|
313
|
|
|
return preg_replace('/\s+/s', '', $matches[ 1 ]) . $matches[ 2 ];
|
|
314
|
|
|
}
|
|
315
|
|
|
|
|
316
|
|
|
// --------------------------------------------------------------------
|
|
317
|
|
|
|
|
318
|
|
|
/**
|
|
319
|
|
|
* Sanitize Naughty HTML
|
|
320
|
|
|
*
|
|
321
|
|
|
* Callback method for xss_clean() to remove naughty HTML elements.
|
|
322
|
|
|
*
|
|
323
|
|
|
* @used-by XSS::clean()
|
|
324
|
|
|
*
|
|
325
|
|
|
* @param array $matches
|
|
326
|
|
|
*
|
|
327
|
|
|
* @return string
|
|
328
|
|
|
*/
|
|
329
|
|
|
protected static function sanitizeNaughtyHTML($matches)
|
|
330
|
|
|
{
|
|
331
|
|
|
// First, escape unclosed tags
|
|
332
|
|
|
if (empty($matches[ 'closeTag' ])) {
|
|
333
|
|
|
return '<' . $matches[ 1 ];
|
|
334
|
|
|
} // Is the element that we caught naughty? If so, escape it
|
|
335
|
|
|
elseif (in_array(strtolower($matches[ 'tagName' ]), self::getConfig('naughty_tags'), true)) {
|
|
|
|
|
|
|
336
|
|
|
return '<' . $matches[ 1 ] . '>';
|
|
337
|
|
|
} // For other tags, see if their attributes are "evil" and strip those
|
|
338
|
|
|
elseif (isset($matches[ 'attributes' ])) {
|
|
339
|
|
|
// We'll store the already fitlered attributes here
|
|
340
|
|
|
$attributes = [];
|
|
341
|
|
|
|
|
342
|
|
|
// Attribute-catching pattern
|
|
343
|
|
|
$attributesPattern = '#'
|
|
344
|
|
|
. '(?<name>[^\s\042\047>/=]+)'
|
|
345
|
|
|
// attribute characters
|
|
346
|
|
|
// optional attribute-value
|
|
347
|
|
|
. '(?:\s*=(?<value>[^\s\042\047=><`]+|\s*\042[^\042]*\042|\s*\047[^\047]*\047|\s*(?U:[^\s\042\047=><`]*)))'
|
|
348
|
|
|
// attribute-value separator
|
|
349
|
|
|
. '#i';
|
|
350
|
|
|
|
|
351
|
|
|
// Blacklist pattern for evil attribute names
|
|
352
|
|
|
$is_evil_pattern = '#^(' . implode('|', self::getConfig('evil_attributes')) . ')$#i';
|
|
353
|
|
|
|
|
354
|
|
|
// Each iteration filters a single attribute
|
|
355
|
|
|
do {
|
|
356
|
|
|
// Strip any non-alpha characters that may preceed an attribute.
|
|
357
|
|
|
// Browsers often parse these incorrectly and that has been a
|
|
358
|
|
|
// of numerous XSS issues we've had.
|
|
359
|
|
|
$matches[ 'attributes' ] = preg_replace('#^[^a-z]+#i', '', $matches[ 'attributes' ]);
|
|
360
|
|
|
|
|
361
|
|
|
if ( ! preg_match($attributesPattern, $matches[ 'attributes' ], $attribute, PREG_OFFSET_CAPTURE)) {
|
|
362
|
|
|
// No (valid) attribute found? Discard everything else inside the tag
|
|
363
|
|
|
break;
|
|
364
|
|
|
}
|
|
365
|
|
|
|
|
366
|
|
|
if (
|
|
367
|
|
|
// Is it indeed an "evil" attribute?
|
|
368
|
|
|
preg_match($is_evil_pattern, $attribute[ 'name' ][ 0 ])
|
|
369
|
|
|
// Or does it have an equals sign, but no value and not quoted? Strip that too!
|
|
370
|
|
|
OR (trim($attribute[ 'value' ][ 0 ]) === '')
|
|
371
|
|
|
) {
|
|
372
|
|
|
$attributes[] = 'xss=removed';
|
|
373
|
|
|
} else {
|
|
374
|
|
|
$attributes[] = $attribute[ 0 ][ 0 ];
|
|
375
|
|
|
}
|
|
376
|
|
|
|
|
377
|
|
|
$matches[ 'attributes' ] = substr(
|
|
378
|
|
|
$matches[ 'attributes' ],
|
|
379
|
|
|
$attribute[ 0 ][ 1 ] + strlen($attribute[ 0 ][ 0 ])
|
|
380
|
|
|
);
|
|
381
|
|
|
} while ($matches[ 'attributes' ] !== '');
|
|
382
|
|
|
$attributes = empty($attributes)
|
|
383
|
|
|
? ''
|
|
384
|
|
|
: ' ' . implode(' ', $attributes);
|
|
385
|
|
|
|
|
386
|
|
|
return '<' . $matches[ 'slash' ] . $matches[ 'tagName' ] . $attributes . '>';
|
|
387
|
|
|
}
|
|
388
|
|
|
|
|
389
|
|
|
return $matches[ 0 ];
|
|
390
|
|
|
}
|
|
391
|
|
|
|
|
392
|
|
|
// --------------------------------------------------------------------
|
|
393
|
|
|
|
|
394
|
|
|
/**
|
|
395
|
|
|
* JS Link Removal
|
|
396
|
|
|
*
|
|
397
|
|
|
* Callback method for xss_clean() to sanitize links.
|
|
398
|
|
|
*
|
|
399
|
|
|
* This limits the PCRE backtracks, making it more performance friendly
|
|
400
|
|
|
* and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
|
|
401
|
|
|
* PHP 5.2+ on link-heavy strings.
|
|
402
|
|
|
*
|
|
403
|
|
|
* @used-by XSS::clean()
|
|
404
|
|
|
*
|
|
405
|
|
|
* @param array $match
|
|
406
|
|
|
*
|
|
407
|
|
|
* @return string
|
|
408
|
|
|
*/
|
|
409
|
|
|
protected static function jsLinkRemoval($match)
|
|
410
|
|
|
{
|
|
411
|
|
|
return str_replace(
|
|
412
|
|
|
$match[ 1 ],
|
|
413
|
|
|
preg_replace(
|
|
414
|
|
|
'#href=.*?(?:(?:alert|prompt|confirm)(?:\(|&\#40;)|javascript:|livescript:|mocha:|charset=|window\.|document\.|\.cookie|<script|<xss|data\s*:)#si',
|
|
415
|
|
|
'',
|
|
416
|
|
|
self::filterAttributes(str_replace(['<', '>'], '', $match[ 1 ]))
|
|
417
|
|
|
),
|
|
418
|
|
|
$match[ 0 ]
|
|
419
|
|
|
);
|
|
420
|
|
|
}
|
|
421
|
|
|
|
|
422
|
|
|
// --------------------------------------------------------------------
|
|
423
|
|
|
|
|
424
|
|
|
/**
|
|
425
|
|
|
* Filter Attributes
|
|
426
|
|
|
*
|
|
427
|
|
|
* Filters tag attributes for consistency and safety.
|
|
428
|
|
|
*
|
|
429
|
|
|
* @used-by Security::jsImgRemoval()
|
|
430
|
|
|
* @used-by Security::jsLinkRemoval()
|
|
431
|
|
|
*
|
|
432
|
|
|
* @param string $str
|
|
433
|
|
|
*
|
|
434
|
|
|
* @return string
|
|
435
|
|
|
*/
|
|
436
|
|
|
protected static function filterAttributes($str)
|
|
437
|
|
|
{
|
|
438
|
|
|
$out = '';
|
|
439
|
|
|
if (preg_match_all('#\s*[a-z\-]+\s*=\s*(\042|\047)([^\\1]*?)\\1#is', $str, $matches)) {
|
|
440
|
|
|
foreach ($matches[ 0 ] as $match) {
|
|
441
|
|
|
$out .= preg_replace('#/\*.*?\*/#s', '', $match);
|
|
442
|
|
|
}
|
|
443
|
|
|
}
|
|
444
|
|
|
|
|
445
|
|
|
return $out;
|
|
446
|
|
|
}
|
|
447
|
|
|
|
|
448
|
|
|
// --------------------------------------------------------------------
|
|
449
|
|
|
|
|
450
|
|
|
/**
|
|
451
|
|
|
* JS Image Removal
|
|
452
|
|
|
*
|
|
453
|
|
|
* Callback method for xss_clean() to sanitize image tags.
|
|
454
|
|
|
*
|
|
455
|
|
|
* This limits the PCRE backtracks, making it more performance friendly
|
|
456
|
|
|
* and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in
|
|
457
|
|
|
* PHP 5.2+ on image tag heavy strings.
|
|
458
|
|
|
*
|
|
459
|
|
|
* @used-by XSS::clean()
|
|
460
|
|
|
*
|
|
461
|
|
|
* @param array $match
|
|
462
|
|
|
*
|
|
463
|
|
|
* @return string
|
|
464
|
|
|
*/
|
|
465
|
|
|
protected static function jsImgRemoval($match)
|
|
466
|
|
|
{
|
|
467
|
|
|
return str_replace(
|
|
468
|
|
|
$match[ 1 ],
|
|
469
|
|
|
preg_replace(
|
|
470
|
|
|
'#src=.*?(?:(?:alert|prompt|confirm)(?:\(|&\#40;)|javascript:|livescript:|mocha:|charset=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si',
|
|
471
|
|
|
'',
|
|
472
|
|
|
self::filterAttributes(str_replace(['<', '>'], '', $match[ 1 ]))
|
|
473
|
|
|
),
|
|
474
|
|
|
$match[ 0 ]
|
|
475
|
|
|
);
|
|
476
|
|
|
}
|
|
477
|
|
|
|
|
478
|
|
|
// --------------------------------------------------------------------
|
|
479
|
|
|
|
|
480
|
|
|
/**
|
|
481
|
|
|
* Attribute Conversion
|
|
482
|
|
|
*
|
|
483
|
|
|
* @used-by XSS::clean()
|
|
484
|
|
|
*
|
|
485
|
|
|
* @param array $match
|
|
486
|
|
|
*
|
|
487
|
|
|
* @return string
|
|
488
|
|
|
*/
|
|
489
|
|
|
protected static function convertAttribute($match)
|
|
490
|
|
|
{
|
|
491
|
|
|
return str_replace(['>', '<', '\\'], ['>', '<', '\\\\'], $match[ 0 ]);
|
|
492
|
|
|
}
|
|
493
|
|
|
|
|
494
|
|
|
// ------------------------------------------------------------------------
|
|
495
|
|
|
|
|
496
|
|
|
/**
|
|
497
|
|
|
* HTML Entity Decode Callback
|
|
498
|
|
|
*
|
|
499
|
|
|
* @used-by XSS::clean()
|
|
500
|
|
|
*
|
|
501
|
|
|
* @param array $match
|
|
502
|
|
|
*
|
|
503
|
|
|
* @return string
|
|
504
|
|
|
*/
|
|
505
|
|
|
protected static function decodeEntity($match)
|
|
506
|
|
|
{
|
|
507
|
|
|
// Protect GET variables in URLs
|
|
508
|
|
|
// 901119URL5918AMP18930PROTECT8198
|
|
509
|
|
|
$match = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-/]+)|i', self::token . '\\1=\\2', $match[ 0 ]);
|
|
|
|
|
|
|
510
|
|
|
|
|
511
|
|
|
$charset = 'UTF-8';
|
|
512
|
|
|
if (function_exists('config')) {
|
|
513
|
|
|
$charset = config()->getItem('charset');
|
|
514
|
|
|
}
|
|
515
|
|
|
|
|
516
|
|
|
// Decode, then un-protect URL GET vars
|
|
517
|
|
|
return str_replace(
|
|
518
|
|
|
self::token,
|
|
519
|
|
|
'&',
|
|
520
|
|
|
self::entityDecode($match, $charset)
|
|
521
|
|
|
);
|
|
522
|
|
|
}
|
|
523
|
|
|
|
|
524
|
|
|
// --------------------------------------------------------------------
|
|
525
|
|
|
|
|
526
|
|
|
/**
|
|
527
|
|
|
* HTML Entities Decode
|
|
528
|
|
|
*
|
|
529
|
|
|
* A replacement for html_entity_decode()
|
|
530
|
|
|
*
|
|
531
|
|
|
* The reason we are not using html_entity_decode() by itself is because
|
|
532
|
|
|
* while it is not technically correct to leave out the semicolon
|
|
533
|
|
|
* at the end of an entity most browsers will still interpret the entity
|
|
534
|
|
|
* correctly. html_entity_decode() does not convert entities without
|
|
535
|
|
|
* semicolons, so we are left with our own little solution here. Bummer.
|
|
536
|
|
|
*
|
|
537
|
|
|
* @link http://php.net/html-entity-decode
|
|
538
|
|
|
*
|
|
539
|
|
|
* @param string $string Input
|
|
540
|
|
|
* @param string $charset Character set
|
|
541
|
|
|
*
|
|
542
|
|
|
* @return string
|
|
543
|
|
|
*/
|
|
544
|
|
|
protected static function entityDecode($string, $charset = null)
|
|
545
|
|
|
{
|
|
546
|
|
|
if (strpos($string, '&') === false) {
|
|
547
|
|
|
return $string;
|
|
548
|
|
|
}
|
|
549
|
|
|
|
|
550
|
|
|
static $entities;
|
|
551
|
|
|
|
|
552
|
|
|
isset($charset) || $charset = 'UTF-8';
|
|
553
|
|
|
|
|
554
|
|
|
if (function_exists('config')) {
|
|
555
|
|
|
$charset = config()->getItem('charset');
|
|
556
|
|
|
}
|
|
557
|
|
|
|
|
558
|
|
|
$flag = ENT_COMPAT | ENT_HTML5;
|
|
559
|
|
|
|
|
560
|
|
|
do {
|
|
561
|
|
|
$comparissonString = $string;
|
|
562
|
|
|
|
|
563
|
|
|
// Decode standard entities, avoiding false positives
|
|
564
|
|
|
if ($c = preg_match_all('/&[a-z]{2,}(?![a-z;])/i', $string, $matches)) {
|
|
565
|
|
|
if ( ! isset($entities)) {
|
|
566
|
|
|
$entities = array_map(
|
|
567
|
|
|
'strtolower',
|
|
568
|
|
|
get_html_translation_table(HTML_ENTITIES, $flag)
|
|
569
|
|
|
);
|
|
570
|
|
|
}
|
|
571
|
|
|
|
|
572
|
|
|
$replace = [];
|
|
573
|
|
|
$matches = array_unique(array_map('strtolower', $matches[ 0 ]));
|
|
574
|
|
|
for ($i = 0; $i < $c; $i++) {
|
|
575
|
|
|
if (($char = array_search($matches[ $i ] . ';', $entities, true)) !== false) {
|
|
576
|
|
|
$replace[ $matches[ $i ] ] = $char;
|
|
577
|
|
|
}
|
|
578
|
|
|
}
|
|
579
|
|
|
|
|
580
|
|
|
$string = str_ireplace(array_keys($replace), array_values($replace), $string);
|
|
581
|
|
|
}
|
|
582
|
|
|
|
|
583
|
|
|
// Decode numeric & UTF16 two byte entities
|
|
584
|
|
|
$string = html_entity_decode(
|
|
585
|
|
|
preg_replace('/(&#(?:x0*[0-9a-f]{2,5}(?![0-9a-f;])|(?:0*\d{2,4}(?![0-9;]))))/iS', '$1;', $string),
|
|
586
|
|
|
$flag,
|
|
587
|
|
|
$charset
|
|
588
|
|
|
);
|
|
589
|
|
|
} while ($comparissonString !== $string);
|
|
590
|
|
|
|
|
591
|
|
|
return $string;
|
|
592
|
|
|
}
|
|
593
|
|
|
|
|
594
|
|
|
} |
o2system /
security
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