The vulnerability in nginx-ui (<= 2.3.5) involves missing authentication on the /mcp_message endpoint of the MCP integration. While the /mcp endpoint requires both IP whitelisting and authentication, /mcp_message only enforces IP whitelisting with a default empty whitelist that permits all IPs. This design flaw allows remote attackers to invoke critical functions without authentication, enabling full control over the nginx service, including configuration changes and service restarts. The CVSS 3.1 base score is 9.8, reflecting network attack vector, no privileges required, no user interaction, and high impact on confidentiality, integrity, and availability. No official patches or fixes are currently available.

An unauthenticated remote attacker can exploit this vulnerability to gain full control over the nginx service managed by nginx-ui. This includes restarting the nginx server, creating, modifying, or deleting configuration files, and triggering automatic reloads of the configuration. Such control can lead to complete compromise of the nginx service, affecting confidentiality, integrity, and availability of the web server environment.

At the time of publication, no official patches or fixes are available for this vulnerability. Users should monitor the vendor's advisory channels for updates. As a temporary mitigation, restricting network access to the /mcp_message endpoint by implementing external network controls such as firewall rules or VPN access may reduce exposure. Avoid exposing the nginx-ui interface to untrusted networks until a patch is released.