Yesterday was not a good day for the macOS developers. In fact we could describe it as the worst day of the operating system, since the error that had to be corrected urgently left the administrator rights completely accessible to any person. I have little doubt that someone had to be fired severely yesterday evening.
And to put the icing on the cake, the patch that Apple released yesterday to solve this error caused another failure preventing correct identification when sharing files on a local network. Fortunately, the same company has already issued a temporary solution while preparing another update.
Corrected identification with a terminal command
This error only occurs with macOS High Sierra, so you should not worry if you have not updated yet. But if you have High Sierra it is very likely that the emergency patch of yesterday was installed automatically. If you have turned on your Mac today and presented the options to share bug reports with Apple, it has happened.
To be able to repair the identification problem when sharing files, we will open a Terminal window (search for "terminal" in Spotlight and you will find the application easily). In it we will write the following command and press ENTER:
sudo / usr / libexec / configureLocalKDC
It will ask for the administrator password, and once you have entered it and pressed INTRO again we can close the Terminal. Now the identification to access shared folders should work. You can read the official Apple guide in English of this solution here.
Hopefully Apple has been able to solve the causes that caused the problems of yesterday and today, and that the next updates of macOS will shine again for your safety.