MacOS High Sierra contains a trivially-exploitable flaw that allows malicious individuals to generate persistent root access accounts, which can affect remotely accessible services such as Remote Desktop and Screen Sharing. To protect yourself, avoid testing this vulnerability on your own system and lock your computer when not in use, or take steps like changing the root password, blocking remote services, and reaching out to security teams if testing was done on a work MacBook. The vulnerability is not known to be remotely exploitable unless you have multiple accounts on your system, including guest accounts, and Remote Desktop is enabled. Apple has pushed a security update to address this issue, and users are encouraged to apply it as soon as possible.