A buffer overflow issue was addressed with improved memory handling. This issue is fixed in macOS Monterey 12.0.1, iOS 15.1 and iPadOS 15.1, watchOS 8.1, tvOS 15.1. Processing maliciously crafted web content may lead to arbitrary code execution.
https://support.apple.com/en-us/HT212876
https://support.apple.com/en-us/HT212874
https://support.apple.com/en-us/HT212869