What’s Vulnerable › Vulnerabilities

CVE-2026-113603: x402 @x402/extensions 2.3.1 through 2.28.0 SIWX Payment Bypass via PaymentPayload.resource

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-20 · updated 2026-10-21
• Weakness: CWE-639

Description

The x402 SIWX server extension in @x402/extensions 2.3.1 through 2.28.0, x402 PyPI 2.11.0 through 2.25.0, and Go module 2.16.0 through 2.28.0 contains an authorization bypass vulnerability that allows paying clients to unlock unpaid routes by supplying a mismatched PaymentPayload.resource URL. Attackers can pay for the cheapest SIWX-protected route while setting resource.url to an expensive route, then repeatedly access it using only a SIGN-IN-WITH-X header without further payment.

Affected products

• x402-foundation github.com/x402-foundation/x402/go/v2: from 2.16.0 through 2.28.0
• x402-foundation x402: from 2.11.0 through 2.25.0
• x402-foundation @x402/extensions: from 2.3.1 through 2.28.0

References

• https://github.com/x402-foundation/x402/blob/go/v2.28.0/go/extensions/signinwithx/server.go
• https://github.com/x402-foundation/x402/blob/npm-@x402/extensions@v2.28.0/typescript/packages/extensions/src/sign-in-with-x/hooks.ts
• https://github.com/x402-foundation/x402/blob/pypi-x402@v2.25.0/python/x402/extensions/sign_in_with_x/hooks.py
• https://github.com/x402-foundation/x402/issues/3838
• https://github.com/x402-foundation/x402/pull/3840
• https://www.vulncheck.com/advisories/x402-x402-extensions-2.3.1-through-2.28.0-siwx-payment-bypass-via-paymentpayload-resource

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