Zero-Trust Runtime Verification for Agentic Payment Protocols: Mitigating Replay and Context-Binding Failures in AP2

Researchers and technology experts published a technical analysis via the arXiv preprint repository in mid-February 2026, introducing a zero-trust runtime verification framework designed to secure the Agent Payments Protocol (AP2) against critical transaction vulnerabilities. As autonomous AI agents increasingly handle commercial transactions without human supervision, the industry has shifted toward mandate-based systems like the Universal Commerce Protocol (UCP) to allow for asynchronous execution. This specific research addresses growing concerns over replay attacks and context-binding failures that could lead to unauthorized financial losses when AI agents interact with payment gateways. The core of the development focuses on moving away from traditional interactive, session-based authorizations, which require a back-and-forth dialogue that hinders AI autonomy. Instead, cryptographically issued mandates allow an agent to prove it has the authority to spend funds within specific limits. However, while the AP2 protocol provides high-level specification guarantees, the researchers identified gaps where actual implementation could diverge from intended security behaviors, necessitating a real-time monitoring solution. The proposed zero-trust runtime verification serves as a defensive layer that constantly validates the state of a transaction against the cryptographic mandate. By ensuring that each payment request is uniquely bound to its specific context—such as the exact vendor, amount, and timestamp—the system prevents malicious actors from capturing a valid mandate and re-using it for unauthorized transactions. This development is seen as a vital step in scaling the 'Agent Economy,' where secure, autonomous machine-to-machine commerce is expected to become a standard part of the global financial infrastructure.