The good news is you have two options to solve this problem right now.  You can change the password of your Root account or you can apply an update that Apple has released today to resolve the issue. You can find details on the High Sierra update on Appleā€™s site.

Brian Krebs provided a good explanation of the issue and the original story around the flaw.  There are reportedly ways this can be remotely exploited as well.

If you are NOT on High Sierra yet you can get ahead of this issue by changing the password before upgrading.