This issue was addressed with improved checks. This issue is fixed in iOS 14.8 and iPadOS 14.8, macOS Big Sur 11.6, Security Update 2021-005 Catalina, tvOS 15, iOS 15 and iPadOS 15, watchOS 8. Processing a maliciously crafted dfont file may lead to arbitrary code execution.
https://support.apple.com/en-us/HT212819
https://support.apple.com/en-us/HT212815
https://support.apple.com/en-us/HT212814
https://support.apple.com/en-us/HT212807
https://support.apple.com/en-us/HT212805
https://support.apple.com/en-us/HT212804
http://seclists.org/fulldisclosure/2021/Oct/63