https://www.theguardian.com/technology/2017/nov/30/apple-macos-high-sierra-fix-breaks-file-sharing-password-security-flaw-emergency-patch

Emergency patch for bug that allowed anyone to take control of a Mac running macOS High Sierra prevented some users from sharing files

In its haste to fix the macOS High Sierra bug that allowed anyone to take control of a Mac computer with a blank password, Apple broke file sharing for some users.