Modern web browsers are complicated, which opens them up to more potential security problems.
The updates have version numbers of iOS 16.4.1, iPadOS 16.4.1, and macOS Ventura 13.3.1, respectively.
That flaw allows for arbitrary code execution with the same provides as kernel code.
Apple says that flaw may also be in use already in the wild.
Source: Apple (iOS/iPadOS,macOS,Safari)