Critical x402 SDK Flaw Could Let Malicious APIs Drain AI Agents’ Token Balances

A vulnerability in the x402 SDK could allow malicious APIs to drain the token balances of AI agents that use the SDK to pay for API calls. This is because the default client in the SDK did not set a spending limit, which could lead to AI agents signing payments for their full token balance if requested. However, this issue was addressed in releases made on August 18, which added a spending limit. The risk is specifically limited to AI agents that automatically sign payments and have apps that do not set spending limits. Affected AI agents could potentially have their token balances depleted by malicious APIs. The security firm V12 disclosed this information on October 22.