Viewing file: xss.php (16.46 KB) -rw-r--r-- Select action/file-type: (+) | (+) | (+) | Code (+) | Session (+) | (+) | SDB (+) | (+) | (+) | (+) | (+) | (+) |
<?php /** * Based on Security class by CodeIgniter * @author ExpressionEngine Dev Team */
class Xcrud_xss { protected $_never_allowed_str = array( 'document.cookie' => '[removed]', 'document.write' => '[removed]', '.parentNode' => '[removed]', '.innerHTML' => '[removed]', 'window.location' => '[removed]', '-moz-binding' => '[removed]', '<!--' => '<!--', '-->' => '-->', '<![CDATA[' => '<![CDATA[', '<comment>' => '<comment>' );
/* never allowed, regex replacement */ /** * List of never allowed regex replacement * * @var array * @access protected */ protected $_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?" );
/** * Constructor * * @return void */ public function __construct() { }
/** * XSS Clean * * Sanitizes data so that Cross Site Scripting Hacks can be * prevented. This function does a fair amount of work but * it is extremely thorough, designed to prevent even the * most obscure XSS attempts. Nothing is ever 100% foolproof, * of course, but I haven't been able to get anything passed * the filter. * * Note: This function should only be used to deal with data * upon submission. It's not something that should * be used for general runtime processing. * * This function was based in part on some code and ideas I * got from Bitflux: http://channel.bitflux.ch/wiki/XSS_Prevention * * To help develop this script I used this great list of * vulnerabilities along with a few other hacks I've * harvested from examining vulnerabilities in other programs: * http://ha.ckers.org/xss.html * * @param mixed string or array * @param bool * @return string */ public function xss_clean($str, $is_image = FALSE) { /* * Is the string an array? * */ if (is_array($str)) { while (list($key) = each($str)) { $str[$key] = $this->xss_clean($str[$key]); }
return $str; }
/* * Remove Invisible Characters */ $str = $this->_remove_invisible_characters($str);
// Validate Entities in URLs $str = $this->_validate_entities($str);
/* * URL Decode * * Just in case stuff like this is submitted: * * <a href="http://%77%77%77%2E%67%6F%6F%67%6C%65%2E%63%6F%6D">Google</a> * * 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. * */
$str = preg_replace_callback("/[a-z]+=([\'\"]).*?\\1/si", array($this, '_convert_attribute'), $str);
$str = preg_replace_callback("/<\w+.*?(?=>|<|$)/si", array($this, '_decode_entity'), $str);
/* * Remove Invisible Characters Again! */ $str = $this->_remove_invisible_characters($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 = $this->_do_never_allowed($str);
/* * Makes PHP tags safe * * Note: XML tags are inadvertently replaced too: * * <?xml * * But it doesn't seem to pose a problem. */ if ($is_image === TRUE) { // Images have a tendency to have the PHP short opening and // closing tags every so often so we skip those and only // do the long opening tags. $str = preg_replace('/<\?(php)/i', "<?\\1", $str); } else { $str = str_replace(array('<?', '?'.'>'), 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', array($this, '_compact_exploded_words'), $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("/<a/i", $str)) { $str = preg_replace_callback("#<a\s+([^>]*?)(>|$)#si", array($this, '_js_link_removal'), $str); }
if (preg_match("/<img/i", $str)) { $str = preg_replace_callback("#<img\s+([^>]*?)(\s?/?>|$)#si", array($this, '_js_img_removal'), $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 = $this->_remove_evil_attributes($str, $is_image);
/* * Sanitize naughty HTML elements * * If a tag containing any of the words in the list * below is found, the tag gets converted to entities. * * So this: <blink> * Becomes: <blink> */ //$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'; $str = preg_replace_callback('#<(/*\s*)('.Xcrud_config::$xss_naughty_html.')([^><]*)([><]*)#is', array($this, '_sanitize_naughty_html'), $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') */ $str = preg_replace('#('.Xcrud_config::$xss_naughty_scripts.')(\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 = $this->_do_never_allowed($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 $str; }
// --------------------------------------------------------------------
/** * HTML Entities Decode * * This function is a replacement for html_entity_decode() * * The reason we are not using html_entity_decode() by itself is because * while it is not technically correct to leave out the semicolon * at the end of an entity most browsers will still interpret the entity * correctly. html_entity_decode() does not convert entities without * semicolons, so we are left with our own little solution here. Bummer. * * @param string * @param string * @return string */ public function entity_decode($str, $charset='UTF-8') { if (stristr($str, '&') === FALSE) { return $str; }
$str = html_entity_decode($str, ENT_COMPAT, $charset); $str = preg_replace('~&#x(0*[0-9a-f]{2,5})~ei', 'chr(hexdec("\\1"))', $str); return preg_replace('~&#([0-9]{2,4})~e', 'chr(\\1)', $str); }
// --------------------------------------------------------------------
/** * Filename Security * * @param string * @param bool * @return string */ public function sanitize_filename($str, $relative_path = FALSE) { $bad = array( "../", "<!--", "-->", "<", ">", "'", '"', '&', '$', '#', '{', '}', '[', ']', '=', ';', '?', "%20", "%22", "%3c", // < "%253c", // < "%3e", // > "%0e", // > "%28", // ( "%29", // ) "%2528", // ( "%26", // & "%24", // $ "%3f", // ? "%3b", // ; "%3d" // = );
if ( ! $relative_path) { $bad[] = './'; $bad[] = '/'; }
$str = $this->_remove_invisible_characters($str, FALSE); return stripslashes(str_replace($bad, '', $str)); }
// ----------------------------------------------------------------
/** * Compact Exploded Words * * Callback function for xss_clean() to remove whitespace from * things like j a v a s c r i p t * * @param type * @return type */ protected function _compact_exploded_words($matches) { return preg_replace('/\s+/s', '', $matches[1]).$matches[2]; }
// --------------------------------------------------------------------
/* * 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: * <a |style=document.write('hello');alert('world');| class=link> * - Everything inside the quotes * For example, everything between the pipes: * <a |style="document.write('hello'); alert('world');"| class="link"> * * @param string $str The string to check * @param boolean $is_image TRUE if this is an image * @return string The string with the evil attributes removed */ protected function _remove_evil_attributes($str, $is_image) { // All javascript event handlers (e.g. onload, onclick, onmouseover), style, and xmlns //$evil_attributes = array('on\w*', 'style', 'xmlns', 'formaction'); $evil_attributes = Xcrud_config::$xss_disalowed_attibutes;
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 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], '/'); }
// 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], '/'); }
// 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$2 $4$6$7$8', $str, -1, $count); }
} while ($count);
return $str; }
// --------------------------------------------------------------------
/** * Sanitize Naughty HTML * * Callback function for xss_clean() to remove naughty HTML elements * * @param array * @return string */ protected function _sanitize_naughty_html($matches) { // encode opening brace $str = '<'.$matches[1].$matches[2].$matches[3];
// encode captured opening or closing brace to prevent recursive vectors $str .= str_replace(array('>', '<'), array('>', '<'), $matches[4]);
return $str; }
// --------------------------------------------------------------------
/** * JS Link Removal * * Callback function for xss_clean() to sanitize links * This limits the PCRE backtracks, making it more performance friendly * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in * PHP 5.2+ on link-heavy strings * * @param array * @return string */ protected function _js_link_removal($match) { return str_replace( $match[1], preg_replace( '#href=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|data\s*:)#si', '', $this->_filter_attributes(str_replace(array('<', '>'), '', $match[1])) ), $match[0] ); }
// --------------------------------------------------------------------
/** * JS Image Removal * * Callback function for xss_clean() to sanitize image tags * This limits the PCRE backtracks, making it more performance friendly * and prevents PREG_BACKTRACK_LIMIT_ERROR from being triggered in * PHP 5.2+ on image tag heavy strings * * @param array * @return string */ protected function _js_img_removal($match) { return str_replace( $match[1], preg_replace( '#src=.*?(alert\(|alert&\#40;|javascript\:|livescript\:|mocha\:|charset\=|window\.|document\.|\.cookie|<script|<xss|base64\s*,)#si', '', $this->_filter_attributes(str_replace(array('<', '>'), '', $match[1])) ), $match[0] ); }
// --------------------------------------------------------------------
/** * Attribute Conversion * * Used as a callback for XSS Clean * * @param array * @return string */ protected function _convert_attribute($match) { return str_replace(array('>', '<', '\\'), array('>', '<', '\\\\'), $match[0]); }
// --------------------------------------------------------------------
/** * Filter Attributes * * Filters tag attributes for consistency and safety * * @param string * @return string */ protected function _filter_attributes($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 $out; }
// --------------------------------------------------------------------
/** * HTML Entity Decode Callback * * Used as a callback for XSS Clean * * @param array * @return string */ protected function _decode_entity($match) { return $this->entity_decode($match[0], strtoupper(Xcrud_config::$mbencoding)); }
// --------------------------------------------------------------------
/** * Validate URL entities * * Called by xss_clean() * * @param string * @return string */ protected function _validate_entities($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);
return $str; }
// ----------------------------------------------------------------------
/** * Do Never Allowed * * A utility function for xss_clean() * * @param string * @return string */ protected function _do_never_allowed($str) { $str = str_replace(array_keys($this->_never_allowed_str), $this->_never_allowed_str, $str);
foreach ($this->_never_allowed_regex as $regex) { $str = preg_replace('#'.$regex.'#is', '[removed]', $str); }
return $str; }
// -------------------------------------------------------------------- protected function _remove_invisible_characters($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; }
}
/* End of file Security.php */ /* Location: ./system/libraries/Security.php */
|