If you haven't yet done so, & you're running High Sierra, please update immediately in order to fix a flaw that would allow root access without entering a password. The patch is called security update 2017-001 & is available via the 'updates' tab in the Mac App Store. If a root account is required, it can be created & a password set using 'System Preferences'. More info at:
It appears, however, that the update introduces a bug re: inability to connect to file shares. A system library was evidently to blame, according to:
Here are the steps:
"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."
It's a small inconvenience when compared to having your machine's root account accessed, believe me! Stay safe. Update now.