Rack::HeadersFilter

Sanitizes some of the "trusted" headers. Useful when you don't control your frontend router like on Heroku. This is the next best thing.

The are some funky heuristics happening inside of Rack::Request. For example request.ip and request.host_with_port use HTTP_X_FORWARDED_HOST which is forgeable by the client on Heroku. This is then trusted by other code like ActionController::ForceSSL as a canonical source of truth. The result is that if something can set the X-Forwarded-Host header, and config.force_ssl = true is set in rails, the user gets redirected to that random host.

This middleware creates a list of "dangerous" headers that are used by Rack::Request and filters out the ones that are not controlled by the router. By default it is configured to be deployed on Heroku.

Installation

Add this line to your application's Gemfile:

gem 'rack-headers_filter'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rack-headers_filter

Usage

This middleware is designed to be installed first in the chain. Either add this to the config.ru:

require 'rack/headers_filter'
use Rack::HeadersFilter

Or in config/environments/production.rb:

# First thing, filter out bad headers (0 == first)
config.middleware.insert_before(0, Rack::HeadersFilter)

By default it is configured with the Heroku router headers. It's also possible to specify them manually:

require 'rack/headers_filter'
use Rack::HeadersFilter, trusted_headers: %w[HTTP_HOST]

Development

After checking out the repo, run script/setup to install dependencies. Then, run rake spec to run the tests. You can also run script/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/pusher/rack-headers_filter.

License

The gem is available as open source under the terms of the MIT License.