This Gist describes various vulnerabilities in "booter sources", i.e. source code that is used for the frontends of "booter"/"stresser" services that offers DDoS attacks on demand.
I'm not sure where this particular source code comes from. I've seen it under the names "vDos Source", "Rage Booter", "Dream Source" and "MHC-Panic Booter Source".
There exists a persistent cross-site scripting vulnerability in the admin/manage.php script. When users sign up, they are asked to input an email address. The email is validated with PHP's FILTER_VALIDATE_EMAIL filter, which is relaxed with the emails that it accepts. The manage.php script, when called, displays the user's email without sanitising or filtering it.