Multiple memory corruption issues were addressed with improved memory handling. This issue affected versions prior to iOS 11.3, tvOS 11.3, watchOS 4.3, Safari 11.1, iTunes 12.7.4 for Windows, iCloud for Windows 7.4.
https://support.apple.com/kb/HT208933
https://support.apple.com/kb/HT208852
https://support.apple.com/kb/HT208698
https://support.apple.com/kb/HT208697
https://support.apple.com/kb/HT208696