Free-Riding in the AI Economy: Demystifying Logic Flaws in x402-Enabled Payment Systems

Computer Science > Cryptography and Security [Submitted on 29 May 2026] Free-Riding in the AI Economy: Demystifying Logic Flaws in x402-Enabled Payment Systems Shengchen Ling, Yihang Huang, Yuan Chen, Yajin Zhou, Lei Wu, Cong Wang The agentic economy demands programmatic financial rails, positioning the x402 protocol as the de facto standard for machine-to-machine payments. However, bridging synchronous HTTP requests with asynchronous blockchain finality introduces profound state synchronization challenges. In this work, we perform the first comprehensive security analysis of the x402 ecosystem. By formalizing five Security Invariants, we reveal that current implementations fail to enforce transactional atomicity and cryptographic context binding, leading to systemic vulnerabilities. We identify a semantic gap in signature design enabling cross-resource substitution, where payment proofs are transplanted to other unauthorized contexts. Furthermore, we expose a temporal gap where concurrency race conditions allow probabilistic service duplication. In the AI inference domain, we demonstrate how dynamic pricing models are vulnerable to allowance overdrafts and infrastructure rate limits. We validate these vulnerabilities against official SDKs and live deployments. Specifically, we show that attackers can exploit the synchronization gap in dynamic authorization schemes to force merchants to subsidize compute costs, achieving a resource leakage ratio of up to 100% on production middleware. Finally, we propose architectural mitigations, advocating for request-bound signatures and pessimistic state locking to secure the financial rails of autonomous agents. All discovered issues have been disclosed to Coinbase and ThirdWeb. Subjects: Cryptography and Security (cs.CR); Computational Engineering, Finance, and Science (cs.CE) Cite as: arXiv:2605.30998 [cs.CR]   (or arXiv:2605.30998v1 [cs.CR] for this version)   https://doi.org/10.48550/arXiv.2605.30998 Focus to learn more Submission history From: Shengchen Ling [view email] [v1] Fri, 29 May 2026 08:31:18 UTC (224 KB) Access Paper: HTML (experimental) view license Current browse context: cs.CR < prev   |   next > new | recent | 2026-05 Change to browse by: cs cs.CE References & Citations NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)