An out-of-bounds read was addressed with improved input validation. This issue is fixed in tvOS 13.3, watchOS 6.1.1, macOS Catalina 10.15.2, Security Update 2019-002 Mojave, and Security Update 2019-007 High Sierra, iOS 13.3 and iPadOS 13.3, iOS 12.4.4, watchOS 5.3.4. Processing malicious video via FaceTime may lead to arbitrary code execution.
https://support.apple.com/en-us/HT210791
https://support.apple.com/en-us/HT210790
https://support.apple.com/en-us/HT210789
https://support.apple.com/en-us/HT210788