IEUrlExtension.php

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<?php
class IEUrlExtension {
        public static function areServerVarsBad( $vars, $extWhitelist = array() ) {
                // Check QUERY_STRING or REQUEST_URI
                if ( isset( $vars['SERVER_SOFTWARE'] )
                        && isset( $vars['REQUEST_URI'] )
                        && self::haveUndecodedRequestUri( $vars['SERVER_SOFTWARE'] ) )
                {
                        $urlPart = $vars['REQUEST_URI'];
                } elseif ( isset( $vars['QUERY_STRING'] ) ) {
                        $urlPart = $vars['QUERY_STRING'];
                } else {
                        $urlPart = '';
                }

                if ( self::isUrlExtensionBad( $urlPart, $extWhitelist ) ) {
                        return true;
                }

                // Some servers have PATH_INFO but not REQUEST_URI, so we check both
                // to be on the safe side.
                if ( isset( $vars['PATH_INFO'] )
                        && self::isUrlExtensionBad( $vars['PATH_INFO'], $extWhitelist ) )
                {
                        return true;
                }

                // All checks passed
                return false;
        }

        public static function isUrlExtensionBad( $urlPart, $extWhitelist = array() ) {
                if ( strval( $urlPart ) === '' ) {
                        return false;
                }

                $extension = self::findIE6Extension( $urlPart );
                if ( strval( $extension ) === '' ) {
                        // No extension or empty extension
                        return false;
                }

                if ( in_array( $extension, array( 'php', 'php5' ) ) ) {
                        // Script extension, OK
                        return false;
                }
                if ( in_array( $extension, $extWhitelist ) ) {
                        // Whitelisted extension
                        return false;
                }

                if ( !preg_match( '/^[a-zA-Z0-9_-]+$/', $extension ) ) {
                        // Non-alphanumeric extension, unlikely to be registered.
                        //
                        // The regex above is known to match all registered file extensions
                        // in a default Windows XP installation. It's important to allow
                        // extensions with ampersands and percent signs, since that reduces
                        // the number of false positives substantially.
                        return false;
                }

                // Possibly bad extension
                return true;
        }

        public static function fixUrlForIE6( $url, $extWhitelist = array() ) {
                $questionPos = strpos( $url, '?' );
                if ( $questionPos === false ) {
                        $beforeQuery = $url . '?';
                        $query = '';
                } elseif ( $questionPos === strlen( $url ) - 1 ) {
                        $beforeQuery = $url;
                        $query = '';
                } else {
                        $beforeQuery = substr( $url, 0, $questionPos + 1 );
                        $query = substr( $url, $questionPos + 1 );
                }

                // Multiple question marks cause problems. Encode the second and
                // subsequent question mark.
                $query = str_replace( '?', '%3E', $query );
                // Append an invalid path character so that IE6 won't see the end of the
                // query string as an extension
                $query .= '&*';
                // Put the URL back together
                $url = $beforeQuery . $query;
                if ( self::isUrlExtensionBad( $url, $extWhitelist ) ) {
                        // Avoid a redirect loop
                        return false;
                }
                return $url;
        }

        public static function findIE6Extension( $url ) {
                $pos = 0;
                $hashPos = strpos( $url, '#' );
                if ( $hashPos !== false ) {
                        $urlLength = $hashPos;
                } else {
                        $urlLength = strlen( $url );
                }
                $remainingLength = $urlLength;
                while ( $remainingLength > 0 ) {
                        // Skip ahead to the next dot
                        $pos += strcspn( $url, '.', $pos, $remainingLength );
                        if ( $pos >= $urlLength ) {
                                // End of string, we're done
                                return false;
                        }

                        // We found a dot. Skip past it
                        $pos++;
                        $remainingLength = $urlLength - $pos;

                        // Check for illegal characters in our prospective extension,
                        // or for another dot
                        $nextPos = $pos + strcspn( $url, "<>\\\"/:|?*.", $pos, $remainingLength );
                        if ( $nextPos >= $urlLength ) {
                                // No illegal character or next dot
                                // We have our extension
                                return substr( $url, $pos, $urlLength - $pos );
                        }
                        if ( $url[$nextPos] === '?' ) {
                                // We've found a legal extension followed by a question mark
                                // If the extension is NOT exe, dll or cgi, return it
                                $extension = substr( $url, $pos, $nextPos - $pos );
                                if ( strcasecmp( $extension, 'exe' ) && strcasecmp( $extension, 'dll' ) &&
                                        strcasecmp( $extension, 'cgi' ) )
                                {
                                        return $extension;
                                }
                                // Else continue looking
                        }
                        // We found an illegal character or another dot
                        // Skip to that character and continue the loop
                        $pos = $nextPos;
                        $remainingLength = $urlLength - $pos;
                }
                return false;
        }

        public static function haveUndecodedRequestUri( $serverSoftware ) {
                static $whitelist = array(
                        'Apache',
                        'Zeus',
                        'LiteSpeed' );
                if ( preg_match( '/^(.*?)($|\/| )/', $serverSoftware, $m ) ) {
                        return in_array( $m[1], $whitelist );
                } else {
                        return false;
                }
        }

}