It says that there is a vulnerability in directory permissions.
I moved to given path, and I found a backup file like the image above. When I unpacked it into the home directory, I got the ssh authentication files.
It seemed to be an ssh authentication file for flag05 account. So I connected with flag05 account. And it worked.(ssh flag05@127.0.0.1).
Input "getflag" command and clear the level.