The discovery of vulnerabilities in embedded firmware has received significant attention from security researchers. However, current vulnerability detection methods still suffer from false negatives and inefficiency, which limit detection effectiveness and require substantial analysis time. To alleviate the above problems, we propose a bidirectional path and data flow analysis method, named BPDA, that effectively compensates for the limitations in detecting firmware vulnerabilities at nonstandard sink points. Our key insight is that, some vulnerabilities arise in nonstandard library sinks, and not all user inputs can reach each corresponding sink. Guided by these insights, we design a more comprehensive sink identification algorithm and leverage accurate backward data flow tracking to eliminate the non-vulnerable paths. After that, we execute forward taint analysis and generate the final Proof of Concepts (PoCs). To evaluate the effectiveness of BPDA, we evaluated it on 84 firmware samples (including both Linux and VxWorks firmware) from 8 major brands, comparing it with state-of-the-art methods (i.e., SaTC and Mango). BPDA discovered 163 real vulnerabilities, including 34 0-day vulnerabilities, of which 32 have been confirmed by CVE/CNVD. Besides, results show that BPDA completed its analysis in just 6% of the time required by SaTC, and remarkably identified 21 vulnerabilities that SaTC and Mango had not detected. It also resolved the issue of Mango failing to analyze specific firmware. In addition, we also performed an ablation study to verify the effectiveness of optimization methods in taint analysis. These results demonstrate the superiority of BPDA in terms of effectiveness and efficiency in detecting embedded firmware vulnerabilities.

The proliferation of taint-style vulnerabilities in embedded devices poses a significant threat to cybersecurity. However, discovering these vulnerabilities is challenging due to their vast number and variety. While current solutions for discovering vulnerabilities in embedded firmware have achieved some success, they suffer from imprecision, are time-consuming, and fail to consider sensitive sinks and constraints. To address these challenges, we propose a novel taint-style vulnerability discovery method called SinkTaint. SinkTaint incorporates backtracking and constraint analysis to achieve high precision and employs a global taint keyword identification strategy to identify implicit taint keywords. It identifies additional sinks using static analysis and performs backtracking analysis to eliminate sanitized sinks, while retrieving the parameter's length for risky sinks. Furthermore, SinkTaint employs dual-label labeling strategies for taint keywords and data, propagating taint labels based on function return values. Finally, SinkTaint employs symbolic execution-based taint analysis to discover taint-style vulnerabilities. We evaluate SinkTaint on datasets released by SaTC and 10 known overflow vulnerabilities. Compared to state-of-the-art methods, including Karonte, SaTC, and EmTaint, SinkTaint demonstrated superior performance, discovering more vulnerabilities with an increase in vulnerability discovery effectiveness by 472%. To date, SinkTaint has identified 21 high-risk taint-style vulnerabilities that were previously undisclosed.