The patch addresses a flaw in its operating system that allows anyone sitting at a Mac to gain administrator access by entering “root” as the username and leaving the password box blank in authentication prompts. This works when altering system settings, logging into the machine, and accessing it remotely via VNC, RDP, screen sharing, and so on. It can also be used to log into system accounts, such as _uucp, and via the command line, which is useful for malware seeking to gain superuser privileges.

If you’re running High Sierra, you’re urged to install the update as soon as possible.

Source: As Apple fixes macOS root password hole, here’s what went wrong • The Register