---
id: CVE-2026-113603
title: >-
  x402 @x402/extensions 2.3.1 through 2.28.0 SIWX Payment Bypass via
  PaymentPayload.resource
summary: >-
  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
  rout…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N'
cvssSource: cna
cwe:
  - CWE-639
vendor: x402-foundation
product: '@x402/extensions'
affected:
  - '@x402/extensions >= 2.3.1 <= 2.28.0'
  - x402 >= 2.11.0 <= 2.25.0
  - github.com/x402-foundation/x402/go/v2 >= 2.16.0 <= 2.28.0
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-21T14:40:26.284069Z'
published: '2026-10-20'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T15:54:28.895Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-113603'
references:
  - url: 'https://github.com/x402-foundation/x402/issues/3838'
  - url: 'https://github.com/x402-foundation/x402/pull/3840'
  - url: >-
      https://github.com/x402-foundation/x402/blob/npm-@x402/extensions@v2.28.0/typescript/packages/extensions/src/sign-in-with-x/hooks.ts
  - url: >-
      https://github.com/x402-foundation/x402/blob/pypi-x402@v2.25.0/python/x402/extensions/sign_in_with_x/hooks.py
  - url: >-
      https://github.com/x402-foundation/x402/blob/go/v2.28.0/go/extensions/signinwithx/server.go
  - url: >-
      https://www.vulncheck.com/advisories/x402-x402-extensions-2.3.1-through-2.28.0-siwx-payment-bypass-via-paymentpayload-resource
    label: >-
      VulnCheck Advisory: x402 @x402/extensions 2.3.1 through 2.28.0 SIWX
      Payment Bypass via PaymentPayload.resource
tags:
  - cve.org
epss: 0.00291
epssPercentile: 0.20495
ingestedAt: '2026-10-20T16:10:53.303Z'
---

## Overview

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

- `@x402/extensions >= 2.3.1 <= 2.28.0`
- `x402 >= 2.11.0 <= 2.25.0`
- `github.com/x402-foundation/x402/go/v2 >= 2.16.0 <= 2.28.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.