A parsing issue in the handling of directory paths was addressed with improved path validation. This issue is fixed in macOS Big Sur 11.3, iOS 14.5 and iPadOS 14.5, watchOS 7.4, tvOS 14.5. A local user may be able to modify protected parts of the file system.
https://support.apple.com/en-us/HT212325
https://support.apple.com/en-us/HT212324