            $q = self::$mysqli->query($vars) ;
            if($q === false) {
                user_error("Query failed: ".self::$mysqli->error."<br />\n$vars"); 
                return false; 
            }
        }
        
        return $q;
    }
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.