I'm not a Rails dev myself but I'm sure a couple of you guys are; there is a bug in Rails that allows an attacker to send requests to a Ruby on Rails server and execute arbitrary commands. Rails users are recommended to update systems to 3.2.11, 3.1.10, 3.0.19, or 2.3.15.
Sources:
http://arstechnica.com/security/2013/01 ... 000-sites/
https://groups.google.com/forum/#!topic ... discussion