Security Digest · Vulnerability record
CVE-2026-46339: 9router: Unauthenticated Remote Code Execution via unprotected MCP custom plugin routes
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.
CVSS 10.0 Critical EPSS 3.4% · p89
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- 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.
From the GitHub advisory
Summary
9router exposes two unauthenticated API endpoints that, when chained together, allow any network-adjacent attacker to execute arbitrary OS commands as the user running the 9router process — with zero prerequisites and no credentials required.
The vulnerability exists because the Next.js middleware that enforces authentication (src/proxy.js) only guards 8 explicitly listed routes. The attack surface of /api/cli-tools/ and /api/mcp/ (40+ routes) receives no authentication whatsoever.
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Root Cause
Weakness type: CWE-78, CWE-306.
Product: 9router (npm) · Assigned by: GitHub_M · Published: 2026-07-15
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| npm | 9router | >= 0.4.30, < 0.4.37 | 0.4.37 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| decolua | 9router | >= 0.4.30, < 0.4.37 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 3.1 | 10 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H |
| GitHub | 3.1 | 10.0 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: changed (can affect other components)
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- 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.
Timeline
- — GitHub-reviewed advisory GHSA-fhh6-4qxv-rpqj published (critical)
- — CVE record published by GitHub_M
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-fhh6-4qxv-rpqj github.com
- CVE.org record CVE-2026-46339 cve.org
- NVD entry CVE-2026-46339 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com