Today, Apple began rolling out iOS 14.4.2, iPadOS 14.4.2, and watchOS 7.3.3, and the company issued an advisory to users to upgrade as soon as possible. Like iOS/iPadOS 14.4.1 before it, this update addresses a security flaw. Additionally, Apple released a similar security update 12.5.2 for older devices like the iPhone 5S or 6 that cannot run iOS 14. The release notes for iOS 14.4.2 and iPadOS 14.4.2 are minimal, simply stating:

This update provides important security updates and is recommended for all users.

For information on the security content of Apple software updates, please visit the website: https://support.apple.com/kb/HT201222

It's that security link that contains the real information.