"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.