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/HT208932
https://support.apple.com/kb/HT208933
https://support.apple.com/kb/HT208934
https://support.apple.com/kb/HT208935