A type confusion 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://www.exploit-db.com/exploits/46298/
https://support.apple.com/HT209448
https://support.apple.com/HT209447
https://support.apple.com/HT209446