macOS Catalina 10.15.5 is a free update that can be downloaded from the Mac App Store using the Update feature in the System Preferences app. There’s also a security update for those running macOS High Sierra.
The first macOS Catalina 10.15.5 update introduced a new Battery Health Management feature designed to extend the overall lifespan of a Mac’s battery by reducing the rate of chemical aging. It also included controls to fine-tune the calibration of the Pro Display XDR and an option to control Automatic Prominence in a Group FaceTime call.
The supplemental update focuses on security fixes and Apple says it should be installed by all users.
macOS Catalina 10.15.5 supplemental update provides important security updates and is recommended for all users.
Some features may not be available for all regions, or on all Apple devices. For detailed information about the security content of this update, please visit: https://support.apple.com/en-us/HT211215
According to the security notes for the update, it addresses a security flaw that could allow an application to execute arbitrary code with kernel privileges.
This is the same vulnerability that has been addressed in today’s iOS 13.5.1, tvOS 13.4.6, and watchOS 6.2.6 updates, and it allowed for the unc0ver jailbreak that allegedly works on all versions of iOS, including iOS 13.5.