An out-of-bounds write issue was addressed with improved bounds checking. This issue is fixed in iOS 13.6 and iPadOS 13.6, macOS Catalina 10.15.6, tvOS 13.4.8, watchOS 6.2.8. Processing a maliciously crafted font file may lead to arbitrary code execution.
https://support.apple.com/kb/HT211291
https://support.apple.com/kb/HT211290