Critical x402 SDK Flaw Could Let Malicious APIs Drain AI Agents’ Token Balances
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Security firm V12 identified three critical flaws in the x402 SDKs used by AI agents to make automated API payments, including a missing spending limit in the default client that could allow malicious APIs to drain an agent's token balance. The TypeScript SDK also accepted Solana token approvals as valid payments, enabling a complete payment bypass, while a flaw in the Sign-In-With-X (SIWx) feature allowed malicious servers to obtain valid login signatures for other websites. All three flaws were patched in releases on August 18, but no public security advisory was issued, and package managers like npm and PyPI did not list the fixes as security updates, leaving developers unaware of the risks.
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