A memory corruption issue was addressed with improved input validation. This issue affected versions prior to iOS 12.1, macOS Mojave 10.14.1, tvOS 12.1, watchOS 5.1, iTunes 12.9.1.
https://support.apple.com/kb/HT209197
https://support.apple.com/kb/HT209195
https://support.apple.com/kb/HT209194