n8n-io/n8n · error · UserError

MCP server " ": URL blocked by SSRF policy

Error message

MCP server "${server.name}": URL blocked by SSRF policy - ${result.error.message}

What it means

The SSRF validator rejected the MCP server's URL — it resolves to a blocked target such as a private/loopback/link-local address, a non-standard port, or a redirected/dns-rebinding-prone destination. The message embeds the validator's own reason; the throw prevents the instance from fetching internal endpoints via MCP config.

Solutions

1. Point the MCP server at a public, routable https endpoint
2. If the internal destination is intentional, ask the admin to allowlist it in the SSRF policy configuration
3. Check for DNS names that resolve to private IPs; use an address the policy permits

When it happens

Trigger: Thrown at packages/@n8n/instance-ai/src/mcp/mcp-client-manager.ts:244 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of n8n-io/n8n@5ac6606e81 (2026-08-12). Data as JSON: /api/errors/1b8f6b1b99cd12db. Report an issue: GitHub.

Appendix: source

Thrown at packages/@n8n/instance-ai/src/mcp/mcp-client-manager.ts:244

			if (!server.url) continue;

			let parsed: URL;
			try {
				parsed = new URL(server.url);
			} catch {
				throw new UserError(`MCP server "${server.name}": invalid URL "${server.url}"`);
			}

			if (parsed.protocol !== 'http:' && parsed.protocol !== 'https:') {
				throw new UserError(
					`MCP server "${server.name}": only http(s) URLs are allowed, got "${parsed.protocol}"`,
				);
			}

			if (this.ssrfValidator) {
				const result = await this.ssrfValidator.validateUrl(server.url);
				if (!result.ok) {
					throw new UserError(
						`MCP server "${server.name}": URL blocked by SSRF policy - ${result.error.message}`,
					);
				}
			}
		}
	}

	private async connectAndListTools(
		configs: McpServerConfig[],
		clientKey: string,
		requireApproval: boolean,
		logger: Logger,
		source: string,
	): Promise<McpRegularToolsResult> {
		const client = new McpClient(
			buildNativeMcpConfigs(configs, requireApproval, this.options.onToolCallSettled),
		);
		this.clientsByKey.set(clientKey, client);

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