https://www.theregister.co.uk/2017/11/28/root_access_bypass_macos_high_sierra/

A trivial-to-exploit flaw in macOS High Sierra, aka macOS 10.13, allows users to gain admin rights, or log in as root, without a password.

The security bug is triggered via the authentication dialog box in Apple's operating system, which prompts you for an administrator's username and password when you need to do stuff like configure privacy and network settings.