9router: Unauthenticated LLM proxy access via /codex rewrite authorization bypass

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.6 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H

EPSS

• CVE-2026-55638: 6.58% estimated exploitation activity in the next 30 days; percentile 93.84 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 9router exposes an OpenAI/Anthropic-compatible LLM proxy. Remote access to this proxy is intended to be protected by an API-key check in the Next.js middleware. However, 9router also defines a rewrite that maps /codex/ to the backend LLM endpoint /api/v1/responses. The middleware authorization decision is made on the incoming request path before the rewrite is applied. Because /codex is not included in the middleware's protected LLM API prefix list, requests to /codex/ bypass the API-key gate and are later rewritten to the same backend used by /api/v1/responses. As a result, an unauthenticated remote attacker can access the LLM proxy through /codex/ and cause the server to make upstream provider calls using the operator-stored LLM provider credentials. Details | Component | File | Note | | ----------------------------- | ----------------------------------- | ------------------------------------------------------------------------- | | Middleware authorization gate |…

Published by the source

28 Aug 2026, 18:32 UTC

Last modified by the source

28 Aug 2026, 18:32 UTC

Source last checked

26 Oct 2026, 13:01 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-8gmq-j984-vp4r

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# Patch Next advisory brief: CVE-2026-55638

Advisory: 9router: Unauthenticated LLM proxy access via /codex rewrite authorization bypass
IDs: CVE-2026-55638, GHSA-8gmq-j984-vp4r
Record: https://patchnext.com/advisories/cve-2026-55638 (revision 1, source checked 26 Oct 2026, 13:01 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: 9router 0.5.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm 9router: affected < 0.5.2; fixed in 0.5.2

## Suggested inspection (read-only)
- `npm ls 9router --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on 9router.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-8gmq-j984-vp4r (GitHub-reviewed advisory GHSA-8gmq-j984-vp4r lists affected ranges: npm 9router >=0 <0.5.2)

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