An out-of-bounds read was addressed with improved bounds checking. This issue is fixed in macOS Big Sur 11.3, iOS 14.5 and iPadOS 14.5, watchOS 7.4, tvOS 14.5. Processing a maliciously crafted image may lead to arbitrary code execution.
https://support.apple.com/en-us/HT212325
https://support.apple.com/en-us/HT212324