Rewrite one of your YAML exploits using the ronin-support library. Some boilerplate code already exists in exploit.rb.
To test your new exploit, go back to the original YAML exploit and start its server:
$ cd ../yaml/level3/
$ ./app.rb
[2013-05-17 18:05:07] INFO WEBrick 1.3.1
[2013-05-17 18:05:07] INFO ruby 1.9.3 (2013-02-22) [x86_64-linux]
== Sinatra/1.3.5 has taken the stage on 9000 for development with backup from WEBrick
[2013-05-17 18:05:07] INFO WEBrick::HTTPServer#start: pid=4037 port=9000
Then draw your sword:
$ ./exploit.rb "puts 'lol'"
[-] Exploiting http://localhost:9000/ ...
[-] Success!
lol
Received #<Callbacks: {"REDACTED"=>[true]}>
localhost.localdomain - - [17/May/2013:18:06:16 PDT] "POST / HTTP/1.1" 200 7
- -> /
Success indeed.