A memory corruption issue was addressed with improved memory handling. This issue affected versions prior to: iOS 12.1, watchOS 5.1.2, tvOS 12.1.1, macOS High Sierra 10.13.6 Security Update 2018-003 High Sierra, macOS Sierra 10.12.6 Security Update 2018-006.
https://support.apple.com/kb/HT209343
https://support.apple.com/kb/HT209342