Update: Apple has pushed out a new version of the root patch, build 17B1002, which appears to fix the file sharing bug. If you don't think you got the updated patch or you're still experiencing file sharing issues, try the fix below.
The recent "root" vulnerability in macOS High Sierra made waves recently because of its wide-reaching security issue. Apple quickly released a security update to fix the issue in record time, but in its haste, may have accidentally caused an annoying, though not security related, bug for some people attempting to file share on Mac. If you are trying to share files on your Mac after installing the security update, Apple has published a help document to fix the issue. Here are the steps.
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:
- Open the Terminal app, which is in the Utilities folder of your Applications folder.
- Type sudo /usr/libexec/configureLocalKDC and press Return.
- Enter your administrator password and press Return.
- Quit the Terminal app.
You should now be able to share files on your Mac without issue.