Auth bypass in Mcp-Router
CVE-2026-81094
The mcp-router CLI served its MCP aggregator on every interface and enforced authentication only when the operator asked for it. The serve command in apps/cli/src/commands/serve.ts defaulted its host to the all-interfaces address on a fixed port, and required a token only when the corresponding flag was supplied, so a default invocation exposed the aggregator, and every MCP server it fronted, to anyone able to reach the port. Release 0.6.3 defaults the host to the loopback address and refuses to start without a token whenever the host it is given is not a loopback address; no earlier release carries either check.
Vulnerability class: Broken Authentication
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
EPSS: 0.006 (47.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 48th percentile — 47.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.006 · change: +0.002
Affected products
Weakness classification (CWE)
References
- github.com/mcp-router/mcp-router (product)
- github.com/mcp-router/mcp-router/security/advisories/GHSA-rx55-5c7h-r56r (vendor-advisory)
- github.com/mcp-router/mcp-router/commit/4c4642cfd274097ec8b33ecd3047390829c79d35 (patch)
- github.com/mcp-router/mcp-router/blob/v0.6.3/apps/cli/src/commands/serve.ts (technical-description)
- www.vulncheck.com/advisories/mcp-router-cli-before-0.6.3-binds-the-mcp-aggregat… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-81094?
- CVE-2026-81094 is a critical-severity vulnerability in Mcp-Router, classified under Missing Authentication for Critical Function. CVSS score: 9.1/10. Published 2026-08-27.
- How severe is CVE-2026-81094?
- Critical severity. CVSS v3 base score is 9.1 out of 10.