The new macOS High Sierra security update ka nn can be downloaded directly from the Mac App Store or through the Mac App Store software update feature on all compatible Macs running macOS High Sierra.
The security update does not give macOS High Sierra a new version number but is called Security Update 2018-001. According to Apple's release notes, Security Update 2018-001 is recommended for all users and is designed to improve the security of macOS. The update fixes two security vulnerabilities associated with the Crash Reporter and LinkPresentation, both of which could be used to gain access to a Mac.
A Safari 11.1 update with fixes for some WebKit vulnerabilities is also included. More information about the contents of the security update may appear in Apple's Support Document Area in a few hours. In a few weeks, macOS High Sierra 10.14 is expected. This planned operating system update includes the iCloud News feature, which is also planned for iOS 11.4.
The feature that was included in the previous betas but was later withdrawn will now appear final. The previous update to MacOS High Sierra 10.13.4 includes support for external GPUs (eGPUs) as well as business chat in news and several other bugfixes and minor feature enhancements, as well as security updates.