A logic issue was addressed with improved state management. This issue is fixed in tvOS 14.6, iOS 14.6 and iPadOS 14.6, Safari 14.1.1, macOS Big Sur 11.4, watchOS 7.5. Processing maliciously crafted web content may lead to universal cross site scripting.
https://support.apple.com/en-us/HT212534
https://support.apple.com/en-us/HT212533
https://support.apple.com/en-us/HT212532