On Tuesday, developer Lemi Ergin, discovered a bug in macOS High Sierra that lets anyone log into an admin account. The way this works if you use the username “root” and no password.
If you want to try this bug, follow these steps.
1. Open System Preferences
2. Choose Users & Groups
3. Click the lock to make changes
4. Type “root” in the username field
5. Move the mouse to the Password field and click there, but leave it blank
6. Click unlock, and it should allow you full access to add a new administrator account.
This allows access from the locked login screen.
An Apple Spokesman told MacRumors that a fix is on the way.
“We are working on a software update to address this issue. In the meantime, setting a root password prevents unauthorized access to your Mac. To enable the Root User and set a password, please follow the instructions here: https://support.apple.com/en-us/HT204012. If a Root User is already enabled, to ensure a blank password is not set, please follow the instructions from the ‘Change the root password’ section.”