x402 Agent payment SDK vulnerability: no spending limit and a silent fix

Security firm V12 published on October 22 an audit of the x402 Agent payment protocol codebase, reporting 25 vulnerabilities, 3 of which are critical severity. The most severe finding is that, before a fix in August 2026, the x402 default payment client set no spending limit of any kind and would accept the first payment option given by the server, with the server deciding the amount, token, payee and network, so a malicious API could require an auto-signing Agent payment wallet to pay the entire balance of a token. The 3 critical vulnerabilities were fixed and released on August 18 and the fixes confirmed on August 20, but as of October 23 the x402 Foundation had not published a security advisory, and the changelog did not label them as security fixes, so npm audit and the PyPI vulnerability list did not flag the last vulnerable version.