Apple released Security Update 2020-002 for High Sierra and Mojave on March 24. Apple also released Catalina 10.5.4 which includes the same security fixes.
In High Sierra, macOS 10.13 the update is found in Apple menu > Mac App Store. In Mojave, macOS 10.14, and Catalina, macOS 10.15, the update is found in Apple menu > System Preferences > Software Update.
Details of these updates can be found in:
As always, it’s wise to apply Apple’s macOS security updates as soon as practical.