An out-of-bounds write issue was addressed with improved bounds checking. This issue is fixed in macOS Big Sur 11.0.1, iOS 14.2 and iPadOS 14.2, tvOS 14.2, watchOS 7.1. Processing a maliciously crafted font file may lead to arbitrary code execution.
https://support.apple.com/en-us/HT211931
https://support.apple.com/en-us/HT211930
https://support.apple.com/en-us/HT211929