Security Update 2018-001 (Sierra and El Capitan)
Apple has released Security Update 2018-001 for macOS 10.12 Sierra and 10.11 El Capitan, patching security vulnerabilities that the company addressed in 10.13.3 High Sierra (see “Apple Releases iOS 11.2.5, macOS 10.13.3, watchOS 4.2.2, and tvOS 11.2.5,” 23 January 2018). Both of the older operating systems also resolve kernel-related issues associated with the Meltdown security vulnerability (see “Apple Releases Meltdown and Spectre Info and Updates,” 5 January 2018), plus a Wi-Fi-related vulnerability that could allow an application to
read restricted memory. Additionally, the security update for 10.12 Sierra deals with a memory corruption issue that could allow arbitrary code execution after processing a maliciously crafted audio file. (Free. For 10.12.6 Sierra, 766.6 MB; for 10.11.6 El Capitan, 863 MB; security content release notes)
Did the patches on a small ElCap iMac lab with no issue at all. The Mac mini server got its OD wrecked though. Oh well.... How useful it is to have a backup boot disk ;-).