Software Engineering Institute

Cable modems are designed to deliver broadband Internet access via unused bandwidth on a cable television network. Some models of Motorola Surfboard cable modems have a web interface that can be used to view log files, check signal levels, restart the modem, and reload the modem's configuration. This web interface listens on a private (RFC 1918) IP address, and can not be accessed via the Internet. Users connected to the modem's LAN interface access the interface via a web browser.

Because the interface uses no authentication, other than binding to a private IP address, the Motorola Surfboard may be vulnerable to various cross-site request forgery (XSRF) vulnerabilities. Note that to exploit these vulnerabilities, an attacker would need to convince a user to visit a specially crafted web page or open an HTML formatted email.

7 April 2016 update: these vulnerabilities have been found to affect more recent and rebranded ARRIS SURFboard SB6141 cable modem gateway products.

A remote, unauthenticated attacker may be able to take any action that an authorized user can including restarting the cable modem, or forcing it to reload its configuration file. While a cable modem is rebooting systems that rely on the affected modem will have limited ability to access the Internet.

We are currently unaware of a practical solution to this problem.

Restrict access

Restricting access to the Surfboard's web interface by using proxy filtering rules, router access control lists or firewall rules will mitigate this vulnerability. To effectively block access, the rules must prevent users on the LAN side of the cable modem from connecting to the web interface's IP address (usually 192.168.100.1).