---
title: "CVE-2026-46339: 9router: Unauthenticated Remote Code Execution via unprotected MCP custom plugin routes"
url: https://erroneo.us/security/cve/CVE-2026-46339/
description: "CVE-2026-46339 (9router (npm)): 9Router is an AI router & token saver. From 0.4.30 until 0.4.37, 9Router's src/proxy.js middleware did not protect…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-07-15
date_modified: 2026-07-16
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-46339"
kev: false
cvss: 10
epss: 0.03352
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-46339: 9router: Unauthenticated Remote Code Execution via unprotected MCP custom plugin routes

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 3.4% , percentile 89: FIRST’s model estimates a 3.4% chance of exploitation activity in the next 30 days, higher than 89% of all scored CVEs (elevated). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes 9router (npm) >= 0.4.30, < 0.4.37, fixed in 0.4.37 . Check your lockfile, including transitive dependencies.

## What it is

9Router is an AI router & token saver. From 0.4.30 until 0.4.37, 9Router's src/proxy.js middleware did not protect /api/cli-tools/ and /api/mcp/, allowing unauthenticated registration of customPlugins through src/app/api/cli-tools/cowork-settings/route.js and command execution through the MCP bridge. This vulnerability is fixed in 0.4.37.

## Affected packages

- npm `9router` >= 0.4.30, < 0.4.37 → fixed: 0.4.37

## Affected products (CVE record)

- decolua 9router: >= 0.4.30, < 0.4.37

## Severity

- GitHub_M CVSS 3.1: 10 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`
- GitHub CVSS 3.1: 10.0 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 3.35% probability of exploitation activity in the next 30 days; percentile 89.

## Sources

- [GitHub Advisory GHSA-fhh6-4qxv-rpqj](https://github.com/advisories/GHSA-fhh6-4qxv-rpqj)
- [CVE.org record CVE-2026-46339](https://www.cve.org/CVERecord?id=CVE-2026-46339)
- [NVD entry CVE-2026-46339](https://nvd.nist.gov/vuln/detail/CVE-2026-46339)
- [github.com](https://github.com/decolua/9router/security/advisories/GHSA-fhh6-4qxv-rpqj)
- [github.com](https://github.com/decolua/9router/commit/992f4db4a0d858bcc86b4786f2abab117a6ccdf8)

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Source page: https://erroneo.us/security/cve/CVE-2026-46339/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt