MyBB Admin Control Code Injection RCE

This exploit module leverages an improper input validation
vulnerability in MyBB prior to `1.8.30` to execute arbitrary code in
the context of the user running the application.

MyBB Admin Control setting page calls PHP `eval` function with an
unsanitized user input. The exploit adds a new setting, injecting the
payload in the vulnerable field, and triggers its execution with a
second request. Finally, it takes care of cleaning up and removes the
setting.

Note that authentication is required for this exploit to work and the
account must have rights to add or update settings (typically, myBB
administrator role).