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<?php |
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/* |
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* This file is part of the Ariadne Component Library. |
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* |
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* (c) Muze <[email protected]> |
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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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namespace arc; |
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/** |
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* noxss is an XSS attack detection and prevention class. It contains two methods, detect and prevent. |
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* The detect() method must be called at the start of handling any request, e.g. in your front loader / router |
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* The prevent() method must be called at the end of handling any request. |
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* |
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* Usage: |
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* <?php |
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* \arc\noxss::detect(); |
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* \\ handle request normally |
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* \arc\noxss::prevent(); |
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* ?> |
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*/ |
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final class noxss |
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{ |
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/** |
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* @var (bool) A flag to indicate if there might be an XSS attack going on |
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*/ |
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public static $potentialXSS = false; |
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/** |
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* @var (array) A container for inputs potentially containing XSS attacks |
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*/ |
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public static $xss; |
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/** |
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* @var (string) buffered output caught by prevent. |
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*/ |
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public static $output; |
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/** |
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* @var (string) Regular expression that matches any input containing quotes, tag start or end delimiters or &. |
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* I don't know any XSS attack that doesn't require at least one of these characters. |
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*/ |
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public static $reXSS = '/[\'"<>&]/'; |
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/** |
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* @var (array) A list of _SERVER variables sent by client header and thus potential attack vectors, can be set |
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* by user when needed / used. |
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*/ |
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public static $xssHeaders = [ 'PHP_AUTH_USER', 'PHP_AUTH_PW' ]; |
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/** |
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* @var (int) Minimum length of an input to qualify as a potential XSS attack. |
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*/ |
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public static $minimumLength = 10; |
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/** |
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* @var (array) A list of inputs to ignore, keyed to the input method - GET, POST, COOKIE, SERVER |
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*/ |
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public static $ignoreList = []; |
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/** |
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* This method checks all user inputs ( get/post/cookie variables, client sent headers ) for potential XSS attacks |
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* If found it flags these and sets self::$potentialXSS to true and starts an output buffer |
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*/ |
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public static function detect() |
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{ |
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foreach ([ 'GET' => $_GET, 'POST' => $_POST, 'COOKIE' => $_COOKIE ] as $method => $inputs) { |
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if (is_array( $inputs )) { |
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self::_gatherXSSInput( $inputs, $method ); |
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} |
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} |
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foreach (self::$xssHeaders as $header) { |
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if (array_key_exists( $header, $_SERVER )) { |
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self::_gatherXSSInput( $_SERVER[$header], 'SERVER' ); |
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} |
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} |
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1 |
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if (!self::$potentialXSS && count( self::$xss )) { |
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// An input with problematic tokens has been spotted, start the output buffer once |
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// to check the output for an occurance of that input _unchanged_ |
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ob_start(); |
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self::$potentialXSS = true; |
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} |
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} |
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private static function _gatherXSSInput($input, $method, $name = null) |
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{ |
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if (is_array( $input )) { |
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foreach ($input as $key => $value) { |
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if (!isset($name)) { |
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self::_gatherXSSInput( $value, $method, $key ); |
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} else { |
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self::_gatherXSSInput( $value, $method, $name ); |
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} |
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} |
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} else { |
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$input = (string) $input; |
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if (( !array_key_exists( $method, self::$ignoreList ) || !array_key_exists( $name, self::$ignoreList[$method] ) ) |
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&& ( strlen( $input ) > self::$minimumLength ) |
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&& preg_match( self::$reXSS, $input, $matches)) |
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{ |
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self::$xss[ $method ][ strlen($input) ][] = $input; |
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} |
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} |
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1 |
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} |
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/** |
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* This method checks if self::$potentialXSS to see if an XSS attack might be going on. If so |
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* the output buffer is ended and the output content retrieved. All inputs flagged as potential XSS attacks |
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* are checked to see if any of these is in the output content _in_unchanged_form_ ! |
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* If so, there is a vulnerability to XSS which is being exploited ( or at least triggered ) and the only |
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* safe option is to not sent the output but sent a 400 Bad Request header instead. |
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* This method doesn't actually send this header but it does throw an exception allowing you to handle it |
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* any way you see fit |
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* |
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* @param callable $f (optional) A method to call when a potential xss attack is detected. Takes one argument: the output |
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* generated by this request so far. If not set prevent() will just sent a 400 Bad Request header if a potential xss attack |
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* is detected. |
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*/ |
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public static function prevent($f = null) |
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{ |
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if (self::$potentialXSS) { |
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self::$output = ob_get_contents(); |
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ob_end_clean(); |
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1 |
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$xssDetected = self::_checkForProblems(); |
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1 |
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if ($xssDetected) { |
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if (is_callable($f)) { |
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$f( self::$output ); |
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} else { |
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header( 'HTTP/1.1 400 Bad Request' ); |
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} |
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} else { |
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echo self::$output; |
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} |
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} |
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1 |
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} |
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private static function _checkForProblems() |
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{ |
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// sort by length of string so longer strings are matched first |
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// key is set to the length of the string by detect() |
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foreach (self::$xss as $inputs) { |
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krsort( $inputs, SORT_NUMERIC ); |
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foreach ($inputs as $values) { |
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if (is_array($values)) { |
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foreach ($values as $value) { |
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if (false !== strpos( self::$output, $value)) { |
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// One of the potential XSS attack inputs has been found _unchanged_ in the output |
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return true; |
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} |
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} |
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} |
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} |
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} |
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return false; |
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} |
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public static function ignore($name, $method = 'GET') |
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{ |
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self::$ignoreList[$method][$name] = 1; |
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} |
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} |
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Ariadne-CMS /
arc-web
