No doubt you've seen this by now if you are running High Sierra,
Pro tip: You can log into macOS High Sierra as root with no password
https://www.theregister.co.uk/2017/11/28/root_access_bypass_macos_high_sierra/
but at least it's been fixed.
https://www.theregister.co.uk/2017/11/29/apple_macos_high_sierra_root_bug_patch/
red faces all round