Auth bypass in X402-Foundation Github.com/x402-Foundation/x402/go/v2
CVE-2026-113603
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.
Vulnerability class: IDOR (Insecure Direct Object Reference)
Published .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- github.com/x402-foundation/x402/issues/3838 (issue-tracking)
- github.com/x402-foundation/x402/pull/3840 (issue-tracking, patch)
- github.com/x402-foundation/x402/blob/npm-@x402/extensions@v2.28.0/typescript/pa… (technical-description)
- github.com/x402-foundation/x402/blob/pypi-x402@v2.25.0/python/x402/extensions/s… (technical-description)
- github.com/x402-foundation/x402/blob/go/v2.28.0/go/extensions/signinwithx/serve… (technical-description)
- www.vulncheck.com/advisories/x402-x402-extensions-2.3.1-through-2.28.0-siwx-pay… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-113603?
- CVE-2026-113603 is a medium-severity vulnerability in X402-Foundation Github.com/x402-Foundation/x402/go/v2, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 6.5/10. Published 2026-10-20.
- How severe is CVE-2026-113603?
- Medium severity. CVSS v3 base score is 6.5 out of 10.