Repair File Sharing After Security Update 2017-001 for macOS High Sierra 10.13.1

Apple pushed a security update for the huge High Sierra vulnerability yesterday, introducing a bug while they were at it. You should install the update as soon as possible and then do this, if File Sharing isn’t working:

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.

John Gruber summarized the problem, which seems to have been around for a few months now:

So the exploit was floating around, under the radar, for weeks at least, but it seems as though no widespread harm came of it.

Personally, I’d call this much too optimistic — people could have been hacked without them even realizing it.