Nginx UI's MCP tool nginx_config_add skips directive validation, allowing authenticated callers to inject nginx directives on the official image to achieve RCE
Nginx UI: MCP nginx_config_add skips config directive validation → authenticated nginx directive injection (RCE on the official image)
The MCP tool nginx_config_add in Nginx UI does not call the configuration validation function, so authenticated MCP callers or agents induced via prompt injection can inject nginx directives that are blocked on other write paths. The project's April 2026 hardening commit wired ValidateConfigFile into api/config/add.go, api/config/modify.go, and mcp/config/config_modify.go, but missed mcp/config/config_add.go. The vulnerability affects versions before 1.9.10-0.20260703131214-23d1934099b0 and is fixed in 1.9.10-0.20260703131214.
The advisory gives the full exploitation chain for the MCP config write tool missing directive validation, which can help teams deploying Nginx UI check whether similar tool call paths also lack validation.