Multiple memory corruption issues were addressed with improved input validation. This issue affected versions prior to iOS 11.4.1, tvOS 11.4.1, watchOS 4.3.2, Safari 11.1.2, iTunes 12.8 for Windows, iCloud for Windows 7.6.
https://support.apple.com/kb/HT208938
https://support.apple.com/kb/HT208936
https://support.apple.com/kb/HT208935
https://support.apple.com/kb/HT208934