Apple on Wednesday released a critical security update to fix a significant security vulnerability that was discovered recently. Some Mac users found that macOS’s login system could be bypassed by using an unexpected user and password combination that would give you access to the contents of any Mac.

An unofficial fix popped up quickly, but Apple released a fast update for the High Sierra operating system that takes care of the bug. Unfortunately, the update ended up breaking different Mac functionality for some users.

Long story short, the root access bug fix broke file sharing for some High Sierra users. Apple acknowledged the new issue in a support document, providing step-by-step instructions on how to fix it:

If you experience issues with authenticating or connecting to file shares on your Mac after you install Security Update 2017-001 for macOS High Sierra 10.13.1, follow these steps to repair file sharing:

  1. Open the Terminal app, which is in the Utilities folder of your Applications folder.
  2. Type sudo /usr/libexec/configureLocalKDC and press Return.
  3. Enter your administrator password and press Return.
  4. Quit the Terminal app.

You should try to see if file sharing actually works on your Mac before trying to fixing the problem, of course. From the looks of it, not all High Sierra users are affected. And it’s very likely that Apple will issue another software update for the issue in the near future, although the problem isn’t as pressing as the severe security flaw that Apple rushed to fix this week.

As for yesterday’s security update, you should download it as fast as possible, especially if other people have physical access to your Mac. Otherwise, your computer can be unlocked by anyone by simply typing “root” as the user and leaving the password field blank.

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