Apple has rushed out an update for the root user vulnerability that was made public yesterday. You should apply this update now!
Available for: macOS High Sierra 10.13.1
Not impacted: macOS Sierra 10.12.6 and earlier
Impact: An attacker may be able to bypass administrator authentication without supplying the administrator’s password
Description: A logic error existed in the validation of credentials. This was addressed with improved credential validation.
Get the update from the Mac App Store app, and find out more about the update here.