Ruby on Rails by default encourages developers to develop insecure web applications. While it’s certainly possible to develop secure sites using the Rails framework you need to be aware of the issues at hand and many technologies that make Rails a powerful easy to use platform will work against you.
Cross Site Request Forgery
CSRF is the new bad guy in web application security. Everyone has worked out how to protect their SQL database from malicious input, and RoR saves you from ever having to worry about this. Cross site scripting attacks are dying and the web community even managed to nip most JSON data leaks in the bud.
Cross Site Request Forgery is very simple. A malicious site asks the user’s browser to carry out an action on a site that the user has an active session on and the victim site carries out that action believing that the user intended that action to occur. In other words the problem arises when a web application relies purely on session cookies to authenticate requests.