GHSA-h6c2-x2m2-mwhf

Summary

The nginx-ui MCP (Model Context Protocol) integration exposes two HTTP endpoints: /mcp and /mcp_message. While /mcp requires both IP whitelisting and authentication (AuthRequired() middleware), the /mcp_message endpoint only applies IP whitelisting - and the default IP whitelist is empty, which the middleware treats as "allow all". This means 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.

Details

Vulnerable Code

mcp/router.go:9-17 - Auth asymmetry between endpoints

func InitRouter(r *gin.Engine) {
	r.Any("/mcp", middleware.IPWhiteList(), middleware.AuthRequired(),
		func(c *gin.Context) {
			mcp.ServeHTTP(c)
		})
	r.Any("/mcp_message", middleware.IPWhiteList(),
		func(c *gin.Context) {
			mcp.ServeHTTP(c)
		})
}

The /mcp endpoint has middleware.AuthRequired(), but /mcp_message does not. Both endpoints route to the same mcp.ServeHTTP() handler, which processes all MCP tool invocations.

internal/middleware/ip_whitelist.go:11-26 - Empty whitelist allows all

func IPWhiteList() gin.HandlerFunc {
	return func(c *gin.Context) {
		clientIP := c.ClientIP()
		if len(settings.AuthSettings.IPWhiteList) == 0 || clientIP == "" || clientIP == "127.0.0.1" || clientIP == "::1" {
			c.Next()
			return
		}
		// ...
	}
}

When IPWhiteList is empty (the default - settings/auth.go initializes Auth{} with no whitelist), the middleware allows all requests through. This is a fail-open design.

Available MCP Tools (all invocable without auth)

From mcp/nginx/:

• restart_nginx - restart the nginx process
• reload_nginx - reload nginx configuration
• nginx_status - read nginx status

From mcp/config/:

• nginx_config_add - create new nginx config files
• nginx_config_modify - modify existing config files -...