This overrides ln itself with a symlink to a shell (or any other executable) that is to be executed as root, useful in case a sudo rule allows to only run ln by path. Warning, this is a destructive action.
If the binary is allowed to run as superuser by sudo, it does not drop the elevated privileges and may be used to access the file system, escalate or maintain privileged access.
sudo ln -fs /bin/sh /bin/ln
sudo ln