This issue was addressed with improved iframe sandbox enforcement. This issue is fixed in macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave. Maliciously crafted web content may violate iframe sandboxing policy.
"Clear History and Website Data" did not clear the history. The issue was addressed with improved data deletion. This issue is fixed in macOS Big Sur 11.1, Security Update 2020-001 Catalina, Security Update 2020-007 Mojave, iOS 14.3 and iPadOS 14.3, tvOS 14.3. A user may be unable to fully delete browsing history.
A code execution vulnerability exists in the WebSocket functionality of Webkit WebKitGTK 2.30.0. A specially crafted web page can trigger a use-after-free vulnerability which can lead to remote code execution. An attacker can get a user to visit a webpage to trigger this vulnerability.