Cable Haunt is a vulnerability in millions of cable modems which allows an attacker to execute arbitrary code on the modem.

This vulnerability is interesting for two reasons – firstly the scale due to the number of vulnerable devices and secondly how the vulnerability came about.

Cable Haunt is a buffer overflow defect in the firmware used in millions of cable modems based on Broadcom chips from different manufacturers and supplied by many different ISP.  The flaw is in the Websockets interface which does not validate the incoming protocol and so allowing arbitrary javascript to send JSON to the endpoint and exploit a buffer overflow.

The firmware can only be updated by the ISP which issued the modem, and so customers are not in control of when the flaw is fixed on their network.

The same flaw is present in devices from different manufacturers because the flaw originally turned up in the reference code supplied by chip manufacturer Broadcom.  Apparently many manufacturers simply copied the reference code into their production firmware and so propagated the flaw.

Reference code is provided by vendors to show a deliberately simple means of using interfaces and API – and often omits error handling code in favour of educational clarity.  Security Managers are well advised to liaise with their colleagues in the software development teams to ensure robust code review and testing procedures are in place and secure coding practices are adopted to prevent similar mistakes in your systems.  (PCI-DSS requires this in Requirement 6: Develop and Maintain secure systems, for example.)   Reference code is not finished code, and should be used with care.

Organisations may be affected by the Cable Haunt vulnerability if their employees home cable modems are compromised resulting in man in the middle attacks when employees are working from home and connecting to the corporate network.