Presentation Material
Abstract
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 then present a series of architectural and practical flaws of TAm and 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 appear secure.
Using Cisco 1001-X series of Trust Anchor enabled routers as a demonstrative platform, we delve into 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 will 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.
AI Generated Summary
This talk presents the Thrangrycat vulnerability, a fundamental flaw in the secure boot implementation of Cisco ASR 1000 series routers and numerous other devices. The research uncovered a hardware-based “trust anchor”—an external Xilinx Spartan-6 FPGA—that independently validates the bootloader firmware. If a modification is detected, the FPGA triggers a hard system reset after approximately 100 seconds, a behavior discovered through electromagnetic emanation analysis.
The core technical contribution is a methodology for reverse-engineering and manipulating proprietary FPGA bitstreams without vendor documentation or tools. The researchers developed techniques to analyze the bitstream format, identify functional blocks (IOBs, BRAM, logic cells), and surgically alter the configuration to disable the malicious reset logic. This involved correlating physical emanation traces with software execution to map the FPGA’s role and then reconstructing its logical function from the raw bitstream.
The practical impact extends far beyond Cisco routers. Any system using FPGAs for critical security functions—including networking gear, automotive systems, and legacy weapons platforms—is potentially vulnerable to similar bitstream manipulation attacks. The researchers released their analysis tools and libraries publicly, enabling the security community to audit and defend against this class of hardware-level bypasses. The work demonstrates that opaque, vendor-managed hardware security components can subvert even robust software-based secure boot chains.