Nginx UI versions up to 2.3.5 expose an unmapped /mcp_message endpoint that bypasses authentication and accepts arbitrary Model Context Protocol commands. By exploiting this unauthenticated endpoint an attacker can perform privileged operations such as creating, deleting, or modifying nginx configuration files, restarting the server, and triggering automatic reloads. This constitutes a full takeover of the nginx service, allowing an attacker to alter the server configuration, halt service availability, or execute code within the nginx process.

The vulnerability affects the Nginx UI application provided by 0xJacky. All releases 2.3.5 and earlier are vulnerable; newer versions – currently unavailable – are presumed to contain the fix.

The CVSS score of 9.8 rates this flaw as critical, and the lack of an available patch increases the risk that an attacker can easily exploit the unauthenticated endpoint from any network location. Although EPSS is not reported and the vulnerability is not listed in KEV, the straightforward network-accessible attack path and full service takeover potential suggest a high likelihood of real-world exploitation.