The research paper “IoT Goes Nuclear: Creating a ZigBee Chain Reaction” by Ronen, O’Flynn, Shamir, and Weingarten garnered moderate media attention (here, here, here, etc) in early November, 2016. As I have worked extensively in ZigBee offensive and defensive security, but never specifically on the ZigBee Light Link (ZLL) profile, I was interested to dig-in and see what the main techniques and issues were, and what lessons other device manufacturers should take away from this disclosure.

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At the 7th Workshop on Embedded Systems Security (WESS 2012), we presented a paper co-authored with myself and researchers at the Dartmouth Trust Lab. You can read a copy of the paper here. Perhaps our abstract gives you a better summary of something I’d write for here:

Any channel crossing the perimeter of a system provides an attack surface to the adversary. Standard network interfaces, such as TCP/IP stacks, constitute one such channel, and security researchers and exploit developers have invested much effort into exploring the attack surfaces and defenses there. However, channels such as USB have been overlooked, even though such code is at least as complexly layered as a network stack, and handles even more complex structures; drivers are notorious as a breeding ground of bugs copy-pasted from boilerplate sample code.

This paper maps out the bus-facing attack surface of a modern operating system, and demonstrates that eective and ecient injection of trac into the buses is real and easily aordable. Further, it presents a simple and inexpensive hardware tool for the job, outlining the architectural and computation-theoretic challenges to creating a defensive OS/driver architecture comparable to that which has been achieved for network stacks.

S. Bratus, T. Goodspeed, P. Johnson, S.W. Smith, R. Speers. “Perimeter-Crossing Buses: a New Attack Surface for Embedded Systems.” 7th Workshop on Embedded Systems Security (WESS 2012). October 2012. To appear.

Immediately following the public release of the Facedancer10 PCBs by neighbors Travis Goodspeed and Sergey Bratus at REcon 2012, I began to develop a Scapy layer to support interacting with the MAX2420 chip used.

The initial code released in the GoodFET repository by Travis has some great examples, one of which is using the Facedancer to emulate a device using the USB HID (human-interface-device) specification. However, when looking at modifying the code to extend it, or use it for fuzzing, a major issue is determining the meaning of fields and the legitimate (and illegitimate) values for them, as well as the relationships between fields. This information is crucial to both specification-compliant use, or fuzzing. Continue reading →