CVE-2026-42449: n8n-mcp's IPv4-mapped IPv6 addresses bypass SSRF protection in validateUrlSync(), enabling full SSRF for SDK embedders

Impact

In the SDK embedder path (N8NDocumentationMCPServer constructor, getN8nApiClient(), and validateInstanceContext()), the synchronous URL validator in SSRFProtection.validateUrlSync() had no IPv6 checks. IPv4-mapped IPv6 addresses such as http://[::ffff:169.254.169.254] bypassed the cloud-metadata, localhost, and private-IP range checks. An attacker able to supply an n8nApiUrl value could cause the server to issue HTTP requests to cloud metadata endpoints (AWS IMDS, GCP, Azure, Alibaba, Oracle), RFC1918 private networks, or localhost services. Response bodies are returned to the caller (non-blind SSRF), and the n8nApiKey is forwarded in the x-n8n-api-key header to the attacker-controlled target.

The first-party HTTP server deployment was not primarily affected — it has a second async validator (validateWebhookUrl) that catches IPv6 addresses.

Impact category: CWE-918 (Server-Side Request Forgery).

Affected

Deployments embedding n8n-mcp as an SDK using N8NDocumentationMCPServer or N8NMCPEngine with user-supplied InstanceContext on versions v2.47.4 through v2.47.13.

Patched

v2.47.14 and later.

• npm: npx n8n-mcp@latest (or pin to >= 2.47.14)
• Docker: docker pull ghcr.io/czlonkowski/n8n-mcp:latest

Workarounds

If developers cannot upgrade immediately:

• Validate URLs before passing to the SDK — reject any n8nApiUrl whose hostname is an IP literal (bracketed IPv6 or dotted IPv4) before calling N8NDocumentationMCPServer / getN8nApiClient(). Accept only URLs with DNS-resolvable hostnames.
• Restrict egress at the network layer — block outbound traffic from the n8n-mcp process to RFC1918 ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), link-local 169.254.0.0/16, and cloud metadata endpoints. Defense-in-depth against this class of issue and recommended even after upgrading.
• Do not accept user-controlled `n8nApiUrl` values — if the project's integration derives the URL from internal configuration only, this vulnerability is not reachable.

Upgrading to v2.47.14 is still strongly recommended.

Credit

Reported by @manthanghasadiya.