A denial of service issue was addressed by removing the vulnerable code. This issue affected versions prior to iOS 12.1.1, macOS Mojave 10.14.2, tvOS 12.1.1, watchOS 5.1.2.
https://support.apple.com/kb/HT209343
https://support.apple.com/kb/HT209342
https://support.apple.com/kb/HT209341