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


- **Severity:** Medium 6.9 (`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`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 20 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** GHSA-vxw2-vmfp-vrg3

## What is CVE-2026-113603?

CVE-2026-113603 is a medium-severity vulnerability in x402-foundation @x402/extensions, published on 20 Oct 2026. 

### Official 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.

Weakness: CWE-639 (Authorization Bypass Through User-Controlled Key)

## Which versions are affected by CVE-2026-113603?


## How do I fix CVE-2026-113603?

No fix has been published for CVE-2026-113603 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-113603 being exploited?

There is no known exploitation of CVE-2026-113603 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-113603 and fix it if it is affected.

What it is: CVE-2026-113603 is a medium-severity vulnerability in x402-foundation @x402/extensions, published on 20 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-113603 in the wild and no public exploit code.

Affected product: x402-foundation @x402/extensions. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-113603/ (Markdown: https://insights.sbomify.com/CVE-2026-113603/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-113603
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-113603
- OSV: https://osv.dev/vulnerability/CVE-2026-113603

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-113603/
Summaries are generated and may contain mistakes; the official description above is the record.