On Zyxel ATP200 ATP500 ATP800 USG20-VPN USG20W-VPN USG40 USG40W USG60 USG60W USG110 USG210 USG310 USG1100 USG1900 USG2200-VPN ZyWALL 110 ZyWALL 310 ZyWALL 1100 devices the security firewall login page is vulnerable to Reflected XSS via the unsanitized 'mp_idx' parameter.