Apple released a supplemental update to macOS Catalina 10.15.5 on Monday afternoon only one week after its official release.
Following an afternoon of updates, Apple's macOS Catalina supplemental update is a simple security update with no special features noted or revealed. The release notes read as follows:
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
The support article Apple referred to stated that a kernel exploit was patched which could allow an application to execute arbitrary code. Apple makes direct reference to the unc0ver exploit that was being used to jailbreak iOS devices in the note.