A memory initialization issue was addressed with improved memory handling. This issue is fixed in iOS 12.1.3,macOS Mojave 10.14.3,tvOS 12.1.2,watchOS 5.1.3. A malicious application may be able to break out of its sandbox.
https://support.apple.com/HT209448
https://support.apple.com/HT209447
https://support.apple.com/HT209446