CVE-2026-45707: n8n-MCP Multi-tenant MCP Requests Fall Back Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-jxx9-px88-pj69",
  "modified" : "2026-06-09T10:28:18Z",
  "published" : "2026-05-18T17:41:42Z",
  "aliases" : [ "CVE-2026-45707" ],
  "summary" : "n8n-MCP: Multi-tenant MCP requests fall back to process-level n8n credentials when tenant headers are absent or incomplete",
  "details" : "## Summary\n\nWhen `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.\n\nThis 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.\n\n## Impact\n\nAn 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.\n\n## Patches\n\nFixed in **n8n-mcp 2.51.2**. The fix:\n\n- Rejects header-less multi-tenant requests at the HTTP edge with HTTP 400 / JSON-RPC `-32602` before any handler runs.\n- Refuses to construct an env-credential n8n API client when `ENABLE_MULTI_TENANT=true`.\n- Closes secondary leak paths in trigger handlers and in the responses of `n8n_health_check`, `n8n_diagnostic`, `n8n_deploy_template`, and `n8n_audit_instance` so the operator's URL and env-key indicator are not surfaced to tenants.\n\nSingle-tenant behavior is unchanged.\n\n## Upgrade\n\n```bash\n# NPM\nnpx n8n-mcp@latest\n\n# Docker\ndocker pull ghcr.io/czlonkowski/n8n-mcp:latest\n```\n\n## Workarounds\n\nIf an immediate upgrade is not possible, any one of the following reduces or eliminates exposure:\n\n- **Disable multi-tenant mode.** Set `ENABLE_MULTI_TENANT=false` (or unset it) and run a separate n8n-mcp instance per tenant with that tenant's own `N8N_API_URL` / `N8N_API_KEY`. This removes the affected code path entirely.\n- **Reject malformed requests at a proxy.** Require both `x-n8n-url` and `x-n8n-key` headers on every request and return 400 if either is missing. Neutralizes the primary header-omission path but does not address the secondary response-shape disclosures, so this is a partial mitigation only.\n- **Reduce the blast radius of the operator API key.** If your n8n instance supports API key scoping (Enterprise, or a Community Edition build that exposes scopes), provision the operator's `N8N_API_KEY` with the minimum scopes required for the operator's own n8n-mcp functions. This does not close the boundary break but limits what a falling-back tenant can do.\n\n## Credit\n\nReported by [@u-ktdi](https://github.com/u-ktdi).",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "n8n-mcp"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.51.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.51.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/czlonkowski/n8n-mcp/security/advisories/GHSA-jxx9-px88-pj69"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-45707"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/czlonkowski/n8n-mcp/commit/853015d0897be7cf2d9d4726de195c938e4395ab"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/czlonkowski/n8n-mcp"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/czlonkowski/n8n-mcp/releases/tag/v2.51.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-284" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-18T17:41:42Z",
    "nvd_published_at" : "2026-05-29T14:16:31Z"
  }
}