A critical vulnerability in Nginx UI with Model Context Protocol (MCP) support is now being exploited in the wild for full server takeover without authentication. The flaw, tracked as CVE-2026-33032, is caused by nginx-ui leaving the ‘/mcp_message’ endpoint unprotected, allowing remote attackers to invoke privileged MCP actions without credentials. Because those actions involve writing and reloading nginx configuration files, a single unauthenticated request can modify server behavior and effectively take over the web server. “[...] any network attacker can invoke all MCP tools without authentication, including restarting nginx, creating/modifying/deleting nginx configuration files, and triggering automatic config reloads – achieving complete nginx service takeover,” reads NIST's descripion of the flaw in the National Vulnerability Database (NVD). NGNIX released a fix for the flaw in version 2.3.4 on March 15, a day after researchers at the AI workflow security company Pluto Security AI reported it. However, the vulnerability identifier, along with technical details and a proof-of-concept (PoC) exploit, emerged at the end of the month. In the CVE Landscape report earlier this week, threat intelligence company Recorded Future notes that CVE-2026-33032 is under active exploitation. Nginx UI is a web-based management interface for the Nginx web server. The library is very popular, with more than 11,000 stars on GitHub and 430,000 Docker pulls. Based on Pluto Security's internet scans using the Shodan engine, there are currently 2,600 publicly exposed instances potentially vulnerable to attacks. Most are in China, the United States, Indonesia, Germany, and Hong Kong.