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.

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.

The EPSS score is 0.00291.

Exploitation none

Automatable yes

Technical Impact partial

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
x402-foundation @x402/extensions unaffected
Version Status Constraints
2.3.1 affected ≤ 2.28.0
x402-foundation x402 unaffected
Version Status Constraints
2.11.0 affected ≤ 2.25.0
x402-foundation github.com/x402-foundation/x402/go/v2 unaffected
Version Status Constraints
2.16.0 affected ≤ 2.28.0

No data.

No data.

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Project Subscriptions

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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/extensions@v2.28.0/typescript/packages/extensions/src/sign-in-with-x/hooks.ts cve-icon cve-icon
https://github.com/x402-foundation/x402/blob/pypi-x402@v2.25.0/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

Wed, 21 Oct 2026 17:15:00 +0000

Type Values Removed Values Added
First Time appeared X402-foundation
X402-foundation x402
Vendors & Products X402-foundation
X402-foundation x402
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

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: 2026-10-21T15:54:28.895Z

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

Link: CVE-2026-113603

cve-icon Vulnrichment

Updated: 2026-10-21T14:40:26.987Z

cve-icon NVD

Status : Awaiting Analysis

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

Modified: 2026-10-21T16:17:23.530

Link: CVE-2026-113603

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-21T16:44:31Z

Weaknesses