by Kastro
Paper/Archive/CVE-2026-81094

CVE-2026-81094

mcp-router mcp-router — mcp-router CLI before 0.6.3 Binds the MCP Aggregator to All Interfaces Without Requiring Authentication

EPSS 0.6%CVSS 9.3
critical.is priorityof 100
38
CVSS 9.3 (CNA)9.3 / 10 × 3027.9Not in CISA KEV+300.0EPSS percentile 49.2.492 × 209.8No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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.

Affected

ProductAffectedFixed inSource
mcp-router< 0.6.30.6.3CNA

Scores by source

VulnCheck (CNA)9.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
VulnCheck (CNA)9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CISA ADPSSVCExploitation: none · Automatable: yes · Technical impact: total

References

refgithub.com/mcp-router/mcp-routeradvisorygithub.com/mcp-router/mcp-router/security/advisories/GHSA-rx55-5c7h-r56rpatchgithub.com/mcp-router/mcp-router/commit/4c4642cfd274097ec8b33ecd3047390829c79d35writeupgithub.com/mcp-router/mcp-router/blob/v0.6.3/apps/cli/src/commands/serve.ts#L105writeupvulncheck.com/advisories/mcp-router-cli-before-0.6.3-binds-the-mcp-aggregator-to-all-interfaces-without-requiring-authentication