A memory corruption issue was addressed with improved input validation. This issue is fixed in tvOS 15, watchOS 8, iOS 15 and iPadOS 15. Processing a maliciously crafted image may lead to arbitrary code execution.
https://support.apple.com/kb/HT212953
https://support.apple.com/kb/HT212869
https://support.apple.com/en-us/HT212819