Apple introduced iOS 12.4.2 to fix a security bug that was found by Google Project Zero. After Tuesday’s launch of iOS 13.1, now seems an odd time to be updating last year’s version, but this patch is for iPhones and iPads made in 2014 and before that can’t upgrade to the new version.
In addition, the company released watchOS 5.3.2 for early Apple Watch models. Plus there’s a fresh security update for macOS Mojave 10.14.6. All take care of the same bug.