Interrupt-oriented Bugdoor Programming: A Minimalist Approach to Bugdooring Embedded Systems Firmware
We demonstrate a simple set of interrupt-related vulnerability primitives that, despite being apparently innocuous, give attackers full control of a microcontroller platform. We then present a novel, minimalist approach to constructing deniable bugdoors for microcontroller firmware, and contrast this approach with the current focus of exploitation research on demonstrations of maximum computational power that malicious computation can achieve. Since the introduction of Return-oriented programming, an ever-increasing number of targets have been demonstrated to unintentionally yield Turing-complete computation environments to attackers controlling the target's various input channels, under ever more restrictive sets of limitations. Yet although modern OS defensive measures indeed require complex computations to bypass, this focus on maximum expressiveness of exploit programming models leads researchers to overlook other research directions for platforms that lack strong defensive measure but occur in mission-critical systems, namely, microcontrollers. In these systems, common exploiter goals such as sensitive code and data exfiltration or arbitrary code execution do not typically require complex computation; instead, a minimal computation is preferred and a simple set of vulnerability primitives typically suffices. We discuss examples of vulnerabilities and the new kinds of tools needed to avoid them in future firmware.
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