Multiple memory corruption issues were addressed with improved memory handling. This issue affected versions prior to iOS 12, tvOS 12, Safari 12, iTunes 12.9 for Windows, iCloud for Windows 7.7.
https://support.apple.com/kb/HT209141
https://support.apple.com/kb/HT209140
https://support.apple.com/kb/HT209109
https://support.apple.com/kb/HT209107
https://support.apple.com/kb/HT209106
https://github.com/WebKit/webkit/commit/a0b0e01648892b0bb60a01aca619eec85eb27f7a