Hmm, there are claims that the High Sierra bug allows remote root access via SSH and screen sharing (neither enabled by default).
Regardless, do this now:
- Open the "Terminal" app
- Run "sudo passwd -u root"
- Enter your own password at three password prompts. This sets the root password to your own, _not_ an empty password.
This takes one minute and then the bug won't affect you. For now, anyway.
https://krebsonsecurity.com/2017/11/macos-high-sierra-users-change-root-password-now/