Check your GitHub account for out of date rails apps following a security update using this handy gist: https://gist.github.com/4492021
git clone https://gist.github.com/4492021.git
gem install octokit
USERNAME=yourusername PASSWORD=yourpassword ruby railscheck.rb
or for checking an orgs repos (that you can access)
USERNAME=yourusername PASSWORD=yourpassword ORG=yourorgname ruby railscheck.rb
It looks for the rails dependency in your Gemfile.lock, which may result in a few false positives where rails is a dependency but you are not using it directly, but it's better to be safe than sorry!