https://arstechnica.com/gadgets/2017/12/updating-macos-can-bring-back-the-nasty-root-security-bug/

The serious and surprising root security bug in macOS High Sierra is back for some users, shortly after Apple declared it fixed. Users who had not installed macOS 10.13.1 and thus were running a prior version of the OS when they received the security update, found that installing 10.13.1 resurfaced the bug, according to a report from Wired.