A memory corruption issue was addressed with improved state management. This issue is fixed in macOS Catalina 10.15, iOS 13, iCloud for Windows 10.7, macOS Catalina 10.15.1, Security Update 2019-001, and Security Update 2019-006, iCloud for Windows 7.14, iTunes 12.10.1 for Windows. Processing maliciously crafted web content may lead to arbitrary code execution.
https://support.apple.com/en-us/HT210722
https://support.apple.com/en-us/HT210637
https://support.apple.com/en-us/HT210636
https://support.apple.com/en-us/HT210635