Software Engineering Institute

Alcatel ADSL modems contain a special account (EXPERT) for gaining privileged access to the device. This account is secured via a challenge-response password authentication mechanism. While the use of such a mechanism is commendable, the algorithm used is not sufficiently strong. Attackers who know the algorithm used to compute the response can compute the correct response using information given to them during the login process.

Because the EXPERT account is accessible via TELNET, HTTP, and FTP, the ADSL modem must have an IP address that is accessible from the Internet to exploit this vulnerability. Alcatel ADSL products do not enable this feature over the wide area network (WAN) interface by default. Note, however, that an attacker with TFTP access may be able to reconfigure the device to enable this feature.

This authentication mechanism is present even if the user has set a user supplied password.

Any problem or vulnerability on your internal network that allows an intruder to communicate with the modem may lead to its compromise, including Trojan horses, compromised systems, or other "bounce" vulnerabilities like the FTP bounce vulnerability described in

http://www.cert.org/tech_tips/ftp_port_attacks.html

Attackers who are able to connect to the ADSL modem can enter a predictable userid and password to gain privileged access to the device. This access can be used to reconfigure the device, potentially introducing additional security weaknesses.

The CERT/CC is currently unaware of a practical solution to this problem.