Google * * Note: Use rawurldecode() so it does not remove plus signs * */ $str = rawurldecode($str); /* * Convert character entities to ASCII * * This permits our tests below to work reliably. * We only convert entities that are within tags since * these are the ones that will pose security problems. * */ $str = preg_replace_callback("/[a-z]+=([\'\"]).*?\\1/si", function($match){ return str_replace(array('>', '<', '\\'), array('>', '<', '\\\\'), $match[0]); }, $str); $str = preg_replace_callback("/<\w+.*?(?=>|<|$)/si", 'self::entity_decode' , $str); /* * Remove Invisible Characters Again! */ $str = self::remove_invisible_characters($str); /* * Convert all tabs to spaces * * This prevents strings like this: ja vascript * NOTE: we deal with spaces between characters later. * NOTE: preg_replace was found to be amazingly slow here on * large blocks of data, so we use str_replace. */ if (strpos($str, "\t") !== FALSE) { $str = str_replace("\t", ' ', $str); } /* * Capture converted string for later comparison */ $converted_string = $str; // Remove Strings that are never allowed $str = self::do_never_allowed($str); /* * Makes PHP tags safe * * Note: XML tags are inadvertently replaced too: * * '), array('<?', '?>'), $str); } /* * Compact any exploded words * * This corrects words like: j a v a s c r i p t * These words are compacted back to their correct state. */ $words = array( 'javascript', 'expression', 'vbscript', 'script', 'base64', 'applet', 'alert', 'document', 'write', 'cookie', 'window' ); foreach ($words as $word) { $temp = ''; for ($i = 0, $wordlen = strlen($word); $i < $wordlen; $i++) { $temp .= substr($word, $i, 1)."\s*"; } // We only want to do this when it is followed by a non-word character // That way valid stuff like "dealer to" does not become "dealerto" $str = preg_replace_callback('#('.substr($temp, 0, -3).')(\W)#is', function($matches){ return preg_replace('/\s+/s', '', $matches[1]).$matches[2]; }, $str); } /* * Remove disallowed Javascript in links or img tags * We used to do some version comparisons and use of stripos for PHP5, * but it is dog slow compared to these simplified non-capturing * preg_match(), especially if the pattern exists in the string */ do { $original = $str; if (preg_match("/]*?)(>|$)#si", function($match){ return str_replace( $match[1], preg_replace( '#href=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|'), '', $match[1])) ), $match[0] ); }, $str); } if (preg_match("/]*?)(\s?/?>|$)#si", function($match){ return str_replace( $match[1], preg_replace( '#src=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|'), '', $match[1])) ), $match[0] ); }, $str); } if (preg_match("/script/i", $str) OR preg_match("/xss/i", $str)) { $str = preg_replace("#<(/*)(script|xss)(.*?)\>#si", '[removed]', $str); } } while($original != $str); unset($original); // Remove evil attributes such as style, onclick and xmlns $str = self::remove_evil_attributes($str, $is_image); /* * Sanitize naughty HTML elements * * If a tag containing any of the words in the list * below is found, the tag gets converted to entities. * * So this: * Becomes: <blink> */ $naughty = 'alert|applet|audio|basefont|base|behavior|bgsound|blink|body|embed|expression|form|frameset|frame|head|html|ilayer|iframe|input|isindex|layer|link|meta|object|plaintext|style|script|textarea|title|video|xml|xss'; $str = preg_replace_callback('#<(/*\s*)('.$naughty.')([^><]*)([><]*)#is', function($matches){ // encode opening brace $str = '<'.$matches[1].$matches[2].$matches[3]; // encode captured opening or closing brace to prevent recursive vectors return $str .= str_replace(array('>', '<'), array('>', '<'), $matches[4]); }, $str); /* * Sanitize naughty scripting elements * * Similar to above, only instead of looking for * tags it looks for PHP and JavaScript commands * that are disallowed. Rather than removing the * code, it simply converts the parenthesis to entities * rendering the code un-executable. * * For example: eval('some code') * Becomes: eval('some code') */ $str = preg_replace('#(alert|cmd|passthru|eval|exec|expression|system|fopen|fsockopen|file|file_get_contents|readfile|unlink)(\s*)\((.*?)\)#si', "\\1\\2(\\3)", $str); // Final clean up // This adds a bit of extra precaution in case // something got through the above filters $str = self::do_never_allowed($str); /* * Images are Handled in a Special Way * - Essentially, we want to know that after all of the character * conversion is done whether any unwanted, likely XSS, code was found. * If not, we return TRUE, as the image is clean. * However, if the string post-conversion does not matched the * string post-removal of XSS, then it fails, as there was unwanted XSS * code found and removed/changed during processing. */ if ($is_image === TRUE) { return ($str == $converted_string) ? TRUE: FALSE; } return $str; }//xss_clean /** * Remove Invisible Characters * * This prevents sandwiching null characters * between ascii characters, like Java\0script. * * @access public * @param string * @return string */ protected static function remove_invisible_characters($str, $url_encoded = TRUE) { $non_displayables = array(); // every control character except newline (dec 10) // carriage return (dec 13), and horizontal tab (dec 09) if ($url_encoded) { $non_displayables[] = '/%0[0-8bcef]/'; // url encoded 00-08, 11, 12, 14, 15 $non_displayables[] = '/%1[0-9a-f]/'; // url encoded 16-31 } $non_displayables[] = '/[\x00-\x08\x0B\x0C\x0E-\x1F\x7F]+/S'; // 00-08, 11, 12, 14-31, 127 do { $str = preg_replace($non_displayables, '', $str, -1, $count); } while ($count); return $str; }//remove_invisible_characters /** * Validate URL entities * * Called by xss_clean() * * @param string * @return string */ protected static function validate_entities($str) { /* * Protect GET variables in URLs */ $xss_hash = md5(time() + mt_rand(0, 1999999999)); $str = preg_replace('|\&([a-z\_0-9\-]+)\=([a-z\_0-9\-]+)|i', $xss_hash."\\1=\\2", $str); /* * Validate standard character entities * * Add a semicolon if missing. We do this to enable * the conversion of entities to ASCII later. * */ $str = preg_replace('#(&\#?[0-9a-z]{2,})([\x00-\x20])*;?#i', "\\1;\\2", $str); /* * Validate UTF16 two byte encoding (x00) * * Just as above, adds a semicolon if missing. * */ $str = preg_replace('#(&\#x?)([0-9A-F]+);?#i',"\\1\\2;",$str); /* * Un-Protect GET variables in URLs */ $str = str_replace($xss_hash, '&', $str); return $str; }//validate_entities /** * Do Never Allowed * * A utility function for xss_clean() * * @param string * @return string */ protected static function do_never_allowed($str) { /** * List of never allowed strings */ $never_allowed_str = array( 'document.cookie' => '[removed]', 'document.write' => '[removed]', '.parentNode' => '[removed]', '.innerHTML' => '[removed]', 'window.location' => '[removed]', '-moz-binding' => '[removed]', '' => '-->', ' '<![CDATA[', '' => '<comment>' ); /** * List of never allowed regex replacement */ $never_allowed_regex = array( 'javascript\s*:', 'expression\s*(\(|&\#40;)', // CSS and IE 'vbscript\s*:', // IE, surprise! 'Redirect\s+302', "([\"'])?data\s*:[^\\1]*?base64[^\\1]*?,[^\\1]*?\\1?" ); $str = str_replace(array_keys($never_allowed_str), $never_allowed_str, $str); foreach ($never_allowed_regex as $regex) { $str = preg_replace('#'.$regex.'#is', '[removed]', $str); } return $str; }//do_never_allowed /* * Remove Evil HTML Attributes (like evenhandlers and style) * * It removes the evil attribute and either: * - Everything up until a space * For example, everything between the pipes: * * - Everything inside the quotes * For example, everything between the pipes: * * * @param string $str The string to check * @param boolean $is_image TRUE if this is an image * @return string The string with the evil attributes removed */ protected static function remove_evil_attributes($str, $is_image) { // All javascript event handlers (e.g. onload, onclick, onmouseover), style, and xmlns $evil_attributes = array('on\w*', 'style', 'xmlns', 'formaction'); if ($is_image === TRUE) { /* * Adobe Photoshop puts XML metadata into JFIF images, * including namespacing, so we have to allow this for images. */ unset($evil_attributes[array_search('xmlns', $evil_attributes)]); } do { $count = 0; $attribs = array(); // find occurrences of illegal attribute strings without quotes preg_match_all('/('.implode('|', $evil_attributes).')\s*=\s*([^\s>]*)/is', $str, $matches, PREG_SET_ORDER); foreach ($matches as $attr) { $attribs[] = preg_quote($attr[0], '/'); } // find occurrences of illegal attribute strings with quotes (042 and 047 are octal quotes) preg_match_all("/(".implode('|', $evil_attributes).")\s*=\s*(\042|\047)([^\\2]*?)(\\2)/is", $str, $matches, PREG_SET_ORDER); foreach ($matches as $attr) { $attribs[] = preg_quote($attr[0], '/'); } // replace illegal attribute strings that are inside an html tag if (count($attribs) > 0) { $str = preg_replace("/<(\/?[^><]+?)([^A-Za-z<>\-])(.*?)(".implode('|', $attribs).")(.*?)([\s><])([><]*)/i", '<$1 $3$5$6$7', $str, -1, $count); } } while ($count); return $str; }//remove_evil_attributes /** * HTML Entities Decode * * This function is a replacement for html_entity_decode() * * The reason we are not using html_entity_decode() by itself is because * while it is not technically correct to leave out the semicolon * at the end of an entity most browsers will still interpret the entity * correctly. html_entity_decode() does not convert entities without * semicolons, so we are left with our own little solution here. Bummer. * * @param string * @param string * @return string */ protected static function entity_decode($arr, $charset='UTF-8') { $str = $arr[0]; if (stristr($str, '&') === FALSE) { return $str; } $str = html_entity_decode($str, ENT_COMPAT, $charset); $str = preg_replace_callback('~&#x(0*[0-9a-f]{2,5})~i', create_function('$matches', 'return chr(hexdec($matches[1]));'), $str); return preg_replace_callback('~&#([0-9]{2,4})~', create_function('$matches', 'return chr($matches[1]);'), $str); }//entity_decode /** * Filter Attributes * * Filters tag attributes for consistency and safety * * @param string * @return string */ protected static function filter_attributes($str) { $out = ''; if (preg_match_all('#\s*[a-z\-]+\s*=\s*(\042|\047)([^\\1]*?)\\1#is', $str, $matches)) { foreach ($matches[0] as $match) { $out .= preg_replace("#/\*.*?\*/#s", '', $match); } } return $out; }//filter_attributes }