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Critical Flaw in x402 SDK Allows Token Drain via Malicious APIs

Critical Flaw in x402 SDK Allows Token Drain via Malicious APIs

First seen 23 Oct 2026, 14:36 UTC • •
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ThreatCluster AI
ThreatCluster •October 23, 2026 at 16:43 UTC
  • •A critical flaw in the x402 SDK allows unauthorized token drainage.
  • •The vulnerability affects AI agents using the SDK without spending limits.
  • •The x402 Foundation has issued patches but has not released a security advisory.

A critical vulnerability in the x402 SDK allows malicious APIs to drain AI agents' token balances by exploiting a lack of spending limits in the default client. Discovered by security firm V12, this flaw enables an attacker to request a payment equal to the full balance of a supported token if the agent's application does not impose limits. The x402 Foundation has patched this issue along with two other critical vulnerabilities in releases dated August 18, 2026. However, as of October 23, 2026, no security advisory has been issued, and npm audit returned no advisories for the affected TypeScript and Python releases. The vulnerabilities affect automated clients and AI agents that use the x402 SDK for API payments, potentially allowing unauthorized access to funds. V12's review identified a total of 25 vulnerabilities, with three rated as critical. No known attacks exploiting these vulnerabilities have been reported to date.

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Timeline

2026-08-18
Patches released for x402 SDK vulnerabilities
The x402 Foundation released updates addressing three critical vulnerabilities, including the spending limit issue.
The Hacker News
2026-10-22
V12 reports critical vulnerabilities in x402 SDK
Security firm V12 disclosed 25 vulnerabilities in the x402 SDK, highlighting three as critical.
v12.sh
2026-10-23
The Hacker News reports on x402 vulnerabilities
The Hacker News published an article detailing the critical flaws and their implications for AI agents.
The Hacker News

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Common questions

What are the critical vulnerabilities in x402 SDK?
The critical vulnerabilities allow unauthorized payments, acceptance of invalid transactions, and unrestricted spending by automated clients.
Have these vulnerabilities been exploited?
No known exploitation has been reported as of now.
What should developers using x402 SDK do?
Developers should update to the latest versions released on August 18, 2026, to mitigate these vulnerabilities.