macOS Sierra Security Update 2018-001 is effectively a minor macOS update which updates a lot of components within macOS – far more than appears necessary to fix the nine security vulnerabilities which Apple lists for it. In all it is about 760 MB in size, which expands to around 2.5 GB of installable files.

It brings new EFI firmware updates for the following models:

• iMac17,1 to 0147 B00
• iMac18,1, iMac18,3 to 0153 B00
• MacBook10,1 to 0156 B00
• MacBook9,1 to 0162 B00
• MacBookPro13,1 to 0215 B00
• MacBookPro13,2, MacBookPro13,3 to 0238 B00
• MacBookPro14,1, MacBookPro14,2, MacBookPro14,3 to 0169 B00.

All other models should also be updated to the same version that ships with High Sierra: you can check those in my full listing of EFI firmware versions. Following this update, all Macs capable of running Sierra and High Sierra should be running new B00 or 00B series EFI firmware which has been updated since September 2017 – a major achievement for Apple’s EFI engineers, and a big step forward for users.

There are also firmware updates for Apple SM0032L SSDs, and some SMC and USB-C hardware.

The only applications updated are Safari, which is brought to version 11.0.3, Bluetooth File Exchange, Grapher, and Keychain Access. However, that does not mean that other apps won’t benefit from bug fixes, as those can still occur in the frameworks and other tools which they use.

Among the other significant updates are WebServer, RAID Utility, most kernel extensions, many frameworks and private frameworks, most of the command tools in /usr/bin, many in /usr/libexec, and many in /usr/sbin.

Another potentially significant update is to Apple’s new file system, APFS. Sierra has had APFS support for a year now, but it had not been updated beyond the test version shipped with 10.12.6 in July 2017. That lagged so far behind the first release in High Sierra in September that there were incompatibilities already apparent. As the gap widened between Sierra’s pre-release and High Sierra’s rapidly-advancing versions, those became more of a problem.

The version number given for APFS in this update is 0.3, which remains well below the current release in High Sierra (which is 748.41.3!). However, this update includes new versions of apfs_util, apfs_invert, apfs_snapshot, fsck_apfs, hfs_convert, mount_apfs, newfs_apfs, and slurpAPFSMeta, together with a new apfs.kext, all of which match those included in the 10.13.3 update. Hopefully these will improve compatibility between the Sierra version of APFS and that in High Sierra 10.13.3.

This update is available from the App Store. A standalone updater is available from here.