Background: With the boosting development of IoT technology, the supply chains of IoT devices become more powerful and sophisticated, and the security issues introduced by code reuse are becoming more prominent. Therefore, the detection and management of vulnerabilities through code similarity detection technology is of great significance for protecting the security of IoT devices. Aim: We aim to propose a more accurate, parallel-friendly, and realistic software supply chain vulnerability detection solution for IoT devices. Method: This paper presents PG-VulNet, standing for Vulnerability-detection Network based on Pseudo-code Graphs. It is a “multi-model” cross-architecture vulnerability detection solution based on pseudo-code and Graph Matching Network (GMN). PG-VulNet extracts both behavioral and structural features of pseudo-code to build customized feature graphs and then uses GMN to detect supply chain vulnerabilities based on these graphs. Results: The experiments show that PG-VulNet achieves an average detection accuracy of 99.14%, significantly higher than existing approaches like Gemini, VulSeeker, FIT, and Asteria. In addition to this, PG-VulNet also excels in detection overhead and false alarms. In the real-world evaluation, PG-VulNet detected 690 known vulnerabilities in 1,611 firmwares. Conclusions: PG-VulNet can effectively detect the vulnerabilities introduced by software supply chain in IoT firmwares and is well suited for large-scale detection. Compared with existing approaches, PG-VulNet has significant advantages.