Maybe try searching again, there are quite a few threats out there. You will need to read up on how to use the exec binding (incl whitelisting commands for version 2.5.3 at least, which you are not, yet, using), maybe this will help as a start (search terms “exec reboot”):
But watch out, I believe this solution does not address the need to whitelist exec commands that was introduced in 2.5.3
