macOS Catalina 10.15.5 Supplemental Update, Security Update 2020-003 High Sierra
https://support.apple.com/en-us/HT211215Released June 1, 2020
Kernel
Available for: macOS High Sierra 10.13.6, macOS Catalina 10.15.5
Impact: An application may be able to execute arbitrary code with kernel privileges
Description: A memory consumption issue was addressed with improved memory handling.
CVE-2020-9859: unc0ver
The current full install for Catalina 10.15.5 includes the supplemental update. THAT makes the 10.15.5 too new. Won't see the 10.15.6 beta 1 update. That should be fixed when the next update (2) is released, maybe later this week.