The new year begins as the old year ended: with yet more vulnerabilities turning up in consumer-grade DSL modems.
A broad hint for any broadband user would be, it seems, to never, ever enable any kind of remote access to the device that connects you to the Internet. However, the hack published by Eloi Vanderbeken at github, here, resets devices to factory default, enabling a remote attack without the password.
Vanderbeken says the backdoor is confirmed in devices from Cisco (under both Cisco and Linksys brands, the latter since offloaded to Belkin), Netgear, Diamond, LevelOne and OpenWAG. According to a post on HackerNews, the common link between the vulnerable devices is that they were manufactured under contract by Sercomm.
Trying to access a Linksys WAG200G device for which he'd forgotten the password, Vanderbeken noticed the device was listening on Port 32764, an undocumented service noted by other users. Reverse engineering the MIPS code the device's firmware is written in, he says he located a way to send commands to the router without being authenticated as an administrator.
In particular, the backdoor allowed him to brute-force a factory reset without providing a password – meaning that on his next login, he had access to everything.
Vanderbeken's proof-of-concept python code includes reporting on whether the device it's running against is vulnerable or not.
It seems to The Register that at least this vulnerability doesn't permit a silent attack: if an outsider ran the code against someone's router, the crash and resulting reset to default passwords would at least alert the victim that something had happened. ®