In addition to the security update released for iOS 11.3.1 today, Apple also released a minor security update for MacOS 10.13.4. The update to High Sierra brings two patches to two vulnerabilities on the platform in a 1GB update. It is available to all Macs running High Sierra.
The first patch has to do with a memory corruption issue in the Crash Reporter that could allow for an application to gain elevated privileges. This issue was found by the Google Project Zero team, Google’s security team that finds issues within Google’s products as well as Apple and Microsoft products.