    function _log($url, $msg) {
        if ($this->_debug) {
            $data = sprintf("[%s] [%s] %s\n", date('r'), $url, $msg);
            $data = strtr($data, '<>', '..');

            $filename = w3_debug_log('varnish');

            return @file_put_contents($filename, $data, FILE_APPEND);
        }

        return true;
    }
The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request.