A use after free issue was addressed with improved memory management. This issue is fixed in macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave, tvOS 14.4, watchOS 7.3, iOS 14.4 and iPadOS 14.4, Safari 14.0.3. Processing maliciously crafted web content may lead to arbitrary code execution.
https://www.debian.org/security/2021/dsa-4923
https://support.apple.com/en-us/HT212152
https://support.apple.com/en-us/HT212149
https://support.apple.com/en-us/HT212148
https://support.apple.com/en-us/HT212147