An integer overflow was addressed with improved input validation. This issue is fixed in iOS 14.5.1 and iPadOS 14.5.1, tvOS 14.6, iOS 12.5.3, Safari 14.1.1, macOS Big Sur 11.3.1. Processing maliciously crafted web content may lead to arbitrary code execution.
https://www.tenable.com/cyber-exposure/2021-threat-landscape-retrospective
https://support.apple.com/en-us/HT212534
https://support.apple.com/en-us/HT212532
https://support.apple.com/en-us/HT212341