9router: Unauthenticated /v1 proxy access via Host-header spoofing → open AI relay + SSRF

Exploitation

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

CVSS

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

EPSS

• CVE-2026-55641: 0.33% estimated exploitation activity in the next 30 days; percentile 25.69 (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's request guard decides a request is "local" (and therefore exempt from API-key auth on the /v1 LLM proxy) by reading the client-controlled Host header. Because 9router binds 0.0.0.0 by default (and the CLI misleadingly prints "localhost"), a remote, unauthenticated attacker who can reach the port can send Host: localhost to be treated as local and obtain /v1 proxy access with no API key, no CLI token, and no dashboard login. In the default configuration (requireApiKey is absent from DEFAULTSETTINGS, so the handler-side key check is skipped), this yields: - Open AI relay — the proxy forwards the attacker's requests to AI providers using the victim's stored paid API keys (cost/quota theft, prompt-based data exfiltration through the victim's accounts). - Unauthenticated SSRF — /v1/search with the built-in noAuth searxng provider takes its outbound fetch URL from the request body (provideroptions.baseUrl), so the attacker drives a server-side fetch to any…

Published by the source

28 Aug 2026, 18:33 UTC

Last modified by the source

28 Aug 2026, 18:34 UTC

Source last checked

26 Oct 2026, 13:01 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-86m2-fcxq-5q7c

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# Patch Next advisory brief: CVE-2026-55641

Advisory: 9router: Unauthenticated `/v1` proxy access via `Host`-header spoofing → open AI relay + SSRF
IDs: CVE-2026-55641, GHSA-86m2-fcxq-5q7c
Record: https://patchnext.com/advisories/cve-2026-55641 (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 8.2)
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-86m2-fcxq-5q7c (GitHub-reviewed advisory GHSA-86m2-fcxq-5q7c lists affected ranges: npm 9router >=0 <0.5.2)

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