An attacker may be able to bypass administrator authentication without supplying the administrator’s password. A logic error existed in the validation of credentials. This was addressed with improved credential validation.
Stop what you’re doing and go install this patch.
Here is Apple’s statement, as relayed by Matthew Panzarino:
Security is a top priority for every Apple product, and regrettably we stumbled with this release of macOS. When our security engineers became aware of the issue Tuesday afternoon, we immediately began working on an update that closes the security hole.
“This morning, as of 8:00 a.m., the update is available for download, and starting later today it will be automatically installed on all systems running the latest version (10.13.1) of macOS High Sierra.”
We greatly regret this error and we apologize to all Mac users, both for releasing with this vulnerability and for the concern it has caused. Our customers deserve better. We are auditing our development processes to help prevent this from happening again.
Here’s a case where Apple forcing an update on systems is a good thing.