Vulnerability arose because the installers fail to check available disk space. As a result, the upgrade could result in devices getting stuck in a boot loop. And if the user’s device has been encrypted using FileVault, the flaw could lead to them being locked out of their data. Apple has released a revised version – macOS Big Sur 11.2.1, 20D7 – that checks for disk space, eliminating the flaw. Apple did not immediately respond to a request for comment.”]
Source: https://www.bankinfosecurity.com/apple-patches-flaw-in-macos-big-sur-upgrade-a-16019