afaik you can't use cross site requests to exploit either the xml bug or the json bug without also exploiting a browser or plugin bug. both issues depend on setting a request header and you are not allowed to do this in the browser security model. but it sucks that CSRF bug becomes RCE bug :(
i actually lied :) there is #from_xml so if you were doing Hash.from_xml(params[:trololol]) or Post.from_xml(params[:lols]) then you would be vulnerable to localhost:3000 attack. but I don't think there is generic attack it would have to be application specific.
