The n8n‑MCP server, which supplies AI assistants with access to n8n node documentation, had a telemetry sanitizer that could leave fragments of URL‑shaped node parameters in data sent to an anonymous telemetry backend. Parameters such as customer or tenant identifiers, short secrets in query strings, and signed request values could be exposed in the stored telemetry, violating the privacy boundaries defined in PRIVACY.md. This represents a moderate confidentiality exposure (CWE‑201).

The vulnerability affects releases of the czlonkowski:n8n‑mcp product that are older than v2.51.3. Systems running the n8n‑MCP server before that version are susceptible; the latest fixed release is v2.51.3. In practice, any deployment of n8n‑MCP that processes workflows containing URL‑shaped parameters is at risk.

With a CVSS score of 6.5 the risk is considered moderate. The EPSS score is not available and the vulnerability is not listed in the CISA KEV catalog, indicating no confirmed exploitation activity. Attackers could trigger the leakage by creating or executing a workflow that includes URL‑shaped parameters; no additional privileged conditions are noted. An adversary with access to a user’s workflow or the ability to execute code in the server could therefore cause sensitive data to be sent to the anonymous telemetry backend.