On 29 November Apple announced that a critical security flaw to its High Sierra Mac operating system (versions 10.13 and 10.13.1). This flaw allows anyone to log in as an administrator without specifying a password. Apple strongly urges that users apply Security Update 2017-001. Apple also notes that after this update is applied, those who need administrative rights to their computers will have to re-enable root access and change the password.
The Guardian has reported that Security Update 2017-001 breaks file sharing, however. Apple has a work-around for this issue involving the Terminal app. Please note, that this work-around requires root (administrative) access to your computer.
Before applying the security update, check the version of your operating system. Sierra 10.12.6 and earlier are unaffected by the security flaw.