The Zoom X3 ADSL modem has a backdoor menu on TCP port 254 that uses the factory default password for access. However, even if the password is changed on the main menu, the backdoor system still allows access with it.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/33724/ZoomX3.txt
Source: https://packetstormsecurity.com/files/33724/ZoomX3.txt.html