n8n-MCP Logs Sensitive Request Data on Unauthorized /mcp Requests

Impact

When n8n-mcp runs in HTTP transport mode, incoming requests to the POST /mcp endpoint had their request metadata written to server logs regardless of the authentication outcome. In deployments where logs are collected, forwarded to external systems, or viewable outside the request trust boundary (shared log storage, SIEM pipelines, support/ops access), this can result in disclosure of:

• bearer tokens from the Authorization header
• per-tenant API keys from the x-n8n-key header in multi-tenant setups
• JSON-RPC request payloads sent to the MCP endpoint

Access control itself was not bypassed — unauthenticated requests were correctly rejected with 401 Unauthorized — but sensitive values from those rejected requests could still be persisted in logs.

Impact category: CWE-532 (Insertion of Sensitive Information into Log File).

Affected

Deployments running n8n-mcp v2.47.10 or earlier in HTTP transport mode (MCP_MODE=http). The stdio transport is not affected.

Patched

v2.47.11 and later.

• npm: npx n8n-mcp@latest (or pin to >= 2.47.11)
• Docker: docker pull ghcr.io/czlonkowski/n8n-mcp:latest

Workarounds

If users cannot upgrade immediately:

• Restrict network access to the HTTP port (firewall, reverse proxy, or VPN) so only trusted clients can reach the endpoint.
• Switch to stdio transport (MCP_MODE=stdio, the default for CLI invocation), which has no HTTP surface.

Credit

n8n-MCP thanks @S4nso (Organization / Jormungandr) for reporting this issue.