rsnapshot version 1.2.0 (and possibly others) allows users to increase their rights on the local filesystem by creating a symlink to a file they want to take control of. rsnapshot will then change the permissions on the file pointed to by that symlink, rather than the symlink itself, when taking a backup.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/37108/rsnapshot_fileperms.txt
Source: https://packetstormsecurity.com/files/37108/rsnapshot_fileperms.txt.html