This issue was addressed with improved checks. This issue is fixed in iOS 14.7, Safari 14.1.2, macOS Big Sur 11.5, watchOS 7.6, tvOS 14.7. Processing maliciously crafted web content may lead to code execution.
https://support.apple.com/en-us/HT212606
https://support.apple.com/en-us/HT212605
https://support.apple.com/en-us/HT212604