https://www.cnet.com/news/fix-for-apples-macos-high-sierra-root-password-flaw-is-here/

Apple's "root" problem has a solution.

The company said on Wednesday that it has issued a software update for the High Sierra version of its MacOS that closes up a glaring vulnerability. The flaw let you log in to any Mac running on High Sierra by simply typing in "root" in the username field and leaving the password blank. The trick gave you system administration access to the computer, allowing you to mess around with other accounts and settings.