CVE-2026-33032 (MCPwn): nginx-ui MCP Authentication Bypass Actively Exploited — CVSS 9.8, One-Line Fix, 2,600 Exposed Instances

Rapid7·high signal

A missing authentication middleware on the /mcp_message endpoint in nginx-ui allows unauthenticated attackers to invoke all MCP tools — restarting nginx, modifying configs, triggering reloads — achieving full server takeover. The default IP whitelist allows all connections. Active exploitation confirmed by Recorded Future (April 13). Listed among 31 most-exploited CVEs. The fix was literally one line of code adding auth middleware. For anyone running MCP endpoints in production: this is a pattern — MCP servers default to permissive access and one forgotten middleware call = full compromise.