A logic issue was addressed with improved state management. This issue is fixed in macOS Big Sur 11.0.1, iOS 14.2 and iPadOS 14.2. Opening a maliciously crafted file may lead to unexpected application termination or arbitrary code execution.
http://seclists.org/fulldisclosure/2020/Dec/26
http://seclists.org/fulldisclosure/2020/Dec/32
https://support.apple.com/en-us/HT211929
https://support.apple.com/en-us/HT211931