Multiple memory corruption issues were addressed with improved memory handling. This issue affected versions prior to iOS 12.1, watchOS 5.1, Safari 12.0.1, iTunes 12.9.1, iCloud for Windows 7.8.
https://support.apple.com/kb/HT209198
https://support.apple.com/kb/HT209197
https://support.apple.com/kb/HT209196