SysFuSS: System-Level Firmware Fuzzing with Selective Symbolic Execution

Abstract: Firmware serves as the critical interface between hardware and software in computing systems, making any bugs or vulnerabilities particularly dangerous as they can cause catastrophic system failures. While fuzzing is a promising approach for identifying design flaws and security vulnerabilities, traditional fuzzers are ineffective at detecting firmware vulnerabilities. For example, existing fuzzers focus on user-level fuzzing, which is not suitable for detecting kernel-level vulnerabilities. Existing fuzzers also face a coverage plateau problem when dealing with complex interactions between firmware and hardware. In this paper, we present an efficient firmware verification framework, SysFuSS, that integrates system-level fuzzing with selective symbolic execution. Our approach leverages system-level emulation for initial fuzzing, and automatically transitions to symbolic execution when coverage reaches a plateau. This strategy enables us to generate targeted test cases that can trigger previously unexplored regions in firmware designs. We have evaluated SysFuSS on real-world embedded firmware, including OpenSSL, WolfBoot, WolfMQTT, HTSlib, MXML, and libIEC. Experimental evaluation demonstrates that SysFuSS significantly outperforms state-of-the-art fuzzers in terms of both branch coverage and detection of firmware vulnerabilities. Specifically, SysFuSS can detect 118 known vulnerabilities while state-of-the-art can cover only 13 of them. Moreover, SysFuSS takes significantly less time (up to 3.3X, 1.7X on average) to activate these vulnerabilities.