100 Seconds of Solitude: Defeating Cisco Trust Anchor With FPGA Bitstream Shenanigans

First commercially introduced in 2013, Cisco Trust Anchor module(TAm) is a proprietary hardware security module that is used in a wide range of Cisco products, including enterprise routers, switches and firewalls. TAm is the foundational root of trust that underpins all other Cisco security and trustworthy computing mechanisms in such devices. We disclose two 0-day vulnerabilities and show a remotely exploitable attack chain that reliably bypasses Cisco Trust Anchor. We present an in-depth analysis of the TAm, from both theoretical and applied perspectives. We present a series of architectural and practical flaws of TAm, describe theoretical methods of attack against such flaws. Next, we enumerate limitations in current state-of-the-art offensive capabilities that made the design of TAm seem secure.

Using Cisco 1001-X series of Trust Anchor enabled routers as a demonstrative platform, we present a detailed analysis of a current implementation of TAm, including results obtained through hardware reverse engineering, Trust Anchor FPGA bitstream analysis, and the reverse engineering of numerous Cisco trustworthy computing mechanisms that depend on TAm. Finally, we present two 0-day vulnerabilities within Cisco IOS and TAm and demonstrate a remotely exploitable attack chain that results in persistent compromise of an up-to-date Cisco router. We discuss the implementation of our TAm bypass, which involves novel methods of reliably manipulating FPGA functionality through bitstream analysis and modification while circumventing the need to perform RTL reconstruction. The use of our methods of manipulation creates numerous possibilities in the exploitation of embedded systems that use FPGAs. While this presentation focuses on the use of our FPGA manipulation techniques in the context of Cisco Trust Anchor, we briefly discuss other uses of our bitstream modification techniques.

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