filelock is a platform-independent file lock for Python. From 4.1.0 until 4.2.1, SoftFileLock can restore a stale marker by name after moving it aside, allowing another local user with rename access in a non-sticky lock directory to swap in a symbolic link and, on a runtime that follows the link and a same-filesystem target, make the lock user hard-link one of its files into the lock directory. This issue is fixed in version 4.2.1.
https://github.com/tox-dev/filelock/security/advisories/GHSA-crv4-6mhj-j5jh
https://github.com/tox-dev/filelock/releases/tag/4.2.1
https://github.com/tox-dev/filelock/pull/843
https://github.com/tox-dev/filelock/commit/740ff666b62a88496c8d7394e4e6230605e4d62b