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BREW-n8n-mcp-CVE-2026-45707 — n8n-MCP: Multi-tenant MCP requests fall back to process-level n8n credentials when tenant headers are absent or incompl…

Affected: Homebrew: n8n-mcp

## Summary

When `ENABLE_MULTI_TENANT=true`, the HTTP transport documents that the target n8n instance is selected per-request from `x-n8n-url` / `x-n8n-key` headers. Requests that omitted those headers — or supplied only one of them — silently fell back to the process-level `N8N_API_URL` / `N8N_API_KEY` credentials configured for the operator's own n8n instance. As a result, an authenticated MCP tenant could cause n8n management calls to execute against the operator's instance instead of its own.

This affects HTTP-mode deployments of `n8n-mcp` that are run as a shared multi-tenant service. Single-tenant deployments (`ENABLE_MULTI_TENANT` unset or `false`) are not affected.

## Impact

An authenticated MCP tenant exploiting this path could read and write workflows, executions, data-table contents, and credential metadata on the operator's n8n instance. If the operator's n8n permits Code-node execution that reaches OS-level modules, the path could escalate to remote code execution inside the operator's n8n runtime. The process-level `N8N_API_KEY` is, in practice, a high-privilege key — Community Edition keys are unscoped by default, and even Enterprise scopes were configured for the operator's own needs and would carry over wholesale to a tenant who triggered the fallback.

## Patches

Fixed in **n8n-mcp 2.51.2**. The fix:

- Rejects header-less multi-tenant requests at the HTTP edge with HTTP 400 / JSON-RPC `-32602` before any handler runs. - Refuses to construct an env-cre…

EUVD-2026-323570

fkie_cve-2026-45707

n8n-MCP is an MCP server that provides AI assistants access to n8n node documentation, properties, and operations. Prior to 2.51.2, when ENABLE_MULTI_TENANT=true, the HTTP transport documents that the target n8n instance is selected per-request from x-n8n-url / x-n8n-key headers. Requests that omitted those headers — or supplied only one of them — silently fell back to the process-level N8N_API_URL / N8N_API_KEY credentials configured for the operator's own n8n instance. As a result, an authenticated MCP tenant could cause n8n management calls to execute against the operator's instance instead of its own. This affects HTTP-mode deployments of n8n-mcp that are run as a shared multi-tenant service. Single-tenant deployments (ENABLE_MULTI_TENANT unset or false) are not affected. This vulnerability is fixed in 2.51.2.