A memory corruption issue was addressed with improved memory handling. This issue is fixed in iOS 15.0.2 and iPadOS 15.0.2, macOS Monterey 12.0.1, iOS 14.8.1 and iPadOS 14.8.1, tvOS 15.1, watchOS 8.1, macOS Big Sur 11.6.1. An application may be able to execute arbitrary code with kernel privileges. Apple is aware of a report that this issue may have been actively exploited..
https://www.tenable.com/cyber-exposure/2021-threat-landscape-retrospective
https://support.apple.com/en-us/HT212876
https://support.apple.com/en-us/HT212874
https://support.apple.com/en-us/HT212872
https://support.apple.com/en-us/HT212869