Along with iOS 12.4.2 Apple is releasing macOS Mojave 10.14.6, a second supplemental update with security fixes.
If you’re running an earlier version of macOS then you will instead find Security Update 2019-005 for macOS High Sierra and Security Update for macOS Sierra available as system software updates.
The security issue as shared here fixes CVE-2019-8641: A remote attacker may be able to cause unexpected application termination or arbitrary code execution.
Check It Out: macOS Mojave 10.14.6 Patches a Security Hole
