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.

Metrics

Attack Vector Network

Attack Complexity Low

Privileges Required None

Attack Requirements None

User Interaction None

Vulnerable System Confidentiality Impact Low

Vulnerable System Integrity Impact Low

Vulnerable System Availability Impact None

Subsequent System Confidentiality Impact None

Subsequent System Integrity Impact None

Subsequent System Availability Impact None

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact Low

Integrity Impact Low

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Affected Vendors & Products

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Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/x402-foundation/x402/blob/go/v2.28.0/go/extensions/signinwithx/server.go cve-icon cve-icon
https://github.com/x402-foundation/x402/blob/npm-@x402/[email protected]/typescript/packages/extensions/src/sign-in-with-x/hooks.ts cve-icon cve-icon
https://github.com/x402-foundation/x402/blob/[email protected]/python/x402/extensions/sign_in_with_x/hooks.py cve-icon cve-icon
https://github.com/x402-foundation/x402/issues/3838 cve-icon cve-icon
https://github.com/x402-foundation/x402/pull/3840 cve-icon cve-icon
https://www.vulncheck.com/advisories/x402-x402-extensions-2.3.1-through-2.28.0-siwx-payment-bypass-via-paymentpayload-resource cve-icon cve-icon
History

Tue, 20 Oct 2026 15:45:00 +0000

Type Values Removed Values Added
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.
Title x402 @x402/extensions 2.3.1 through 2.28.0 SIWX Payment Bypass via PaymentPayload.resource
Weaknesses CWE-639
References
Metrics cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N'}

cvssV4_0

{'score': 6.9, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published:

Updated: 2026-10-20T15:40:30.742Z

Reserved: 2026-10-20T11:48:49.343Z

Link: CVE-2026-113603

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-20T16:17:10.087

Modified: 2026-10-20T20:06:37.150

Link: CVE-2026-113603

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-20T17:30:13Z

Weaknesses