I was using Facets today to find vulnerabilities in my Gemfile and 5 out of 6 are in the Rails gem.
I'm using Rails 4.0.0 and there seems to be a lot of vulnerabilities in this version so I head over to github/rails, click on
4-0-stable and locate the
RAILS_VERSION file. At the time I'm writing this Rails is stable at
To update Rails, you need to change its version in
gem 'rails', '4.0.2'
$ bundle update rails
in your command line. Don't forget to run your tests!