Apple has released MacOS Big Sur 11.4 with fixes for at least 73 security issues.
Apple has also released security updates for MacOS Catalina and MacOS Mojave, along with an update for Safari 14.1.1 that should be installed using the Mac App Store.
These updates contain fixes for critical vulnerabilities that could be exploited to take control of a vulnerable system.
Users should update as soon as possible to avoid potential exploitation.
Important links for MacOS Catalina and MacOS Mojave users:
How to update MacOS
Security Update 2021-003 Catalina Release Notes
Security Update 2021-004 Mojave Release Notes
How to update Safari
Safari 14.1.1 Release Notes