On November 29th 2017 Apple released a critical security update (Security Update 2017-001) to fix a major vulnerability. If you have not yet installed the security fix, we highly recommend you do so.

After installing this critical security update some users have found that their File Sharing was broken. Apple has acknowledged the issue and have provided the following instructions on how to resolve the issue. (see https://support.apple.com/en-us/HT208317)

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.

Apple will most likely release a fix for the issue in the future but there is no date scheduled yet.