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://github.com/WebKit/webkit/commit/a0b0e01648892b0bb60a01aca619eec85eb27f7a
https://support.apple.com/kb/HT209106
https://support.apple.com/kb/HT209107
https://support.apple.com/kb/HT209109