A stack overflow was addressed with improved input validation. This issue is fixed in iOS 14.7, macOS Big Sur 11.5, watchOS 7.6, tvOS 14.7, Security Update 2021-005 Mojave, Security Update 2021-004 Catalina. Processing a maliciously crafted font file may lead to arbitrary code execution.
https://support.apple.com/en-us/HT212605
https://support.apple.com/en-us/HT212604
https://support.apple.com/en-us/HT212603
https://support.apple.com/en-us/HT212602