Apple explains how to fix macOS High Sierra file sharing after security update breaks feature

Though today's macOS High Sierra security update patched a critical root user bug, it introduced a problem that prevents Mac users from authenticating or connecting to file shares on their Mac.

Briefly outlined in a document posted to Apple's Support pages, the issue appears to impact only a portion of macOS High Sierra users who downloaded and installed today's security update.

The number of people affected by the file sharing bug is unknown, but it seems a system library error is to blame for failed authentications. Impacted users took to social media to report the problem, which is quickly solved with a minor Terminal procedure.

As noted by Apple in its Support Document, users experiencing file sharing issues need to do the following:

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.

That Apple introduced a second issue with its fix for the recently discovered root access bug is unfortunate, but the remedy is a small price to pay to ensure that your Mac is secure.

On Tuesday, researchers went public with a macOS High Sierra flaw that allows anyone to log in as a Mac's "root" System Administrator without requiring a password. Using the same method, nefarious users can also bypass the macOS lock screen and, in some cases, gain root access to a Mac remotely if certain screen sharing, remote access or VNC sessions are enabled.

Apple promised a fix just hours after the security hole hit media outlets. The company delivered the patch early today as Security Update 2017-001, which was made available through the Mac App Store.