https://www.theregister.co.uk/2019/10/30/apple_security_patches_catalina_macos_ios/

Apple has released patches for the hated macOS Catalina – but not to fix the operating system's UI failures. These are security updates also affecting iOS and Apple Watches, and include one that prevents a remote attacker from executing code on your iThings.

Affecting macOS Catalina 10.15, Mojave 10.14.6 and High Sierra 10.13.6, the most serious of these vulnerabilities could allow an attacker to access protected areas of memory, gain elevated privileges and execute arbitrary code on the system or cause denial-of-service conditions.