Rack::ContentSecurityPolicy

Rack::ContentSecurityPolicy is a Rack middleware that makes it easy for your Rack based application (Sinatra, Rails) to serve an Content-Security-Policy or Content-Security-Policy-Report-Only header.

This middleware was inspired by the p0deje/content-security-policy middleware and borrows quite a bit of code from that gem. This gem also makes extensive use of the contracts gem to enforce strict type checking and validation on all inputs and outputs. It is designed to fail-fast on errors.

It provides full support for Content Security Policy Level 1/2/3 directives.

Add this line to your application's Gemfile:

gem 'rack-content_security_policy', '~> 0.1'

And then execute:

$ bundle install

Or install it directly with:

$ gem install rack-content_security_policy

This middleware can be configured with a block or a hash of config options. It accepts two primary configuration options:

• report_only : boolean true or false. Returns a Content-Security-Policy-Report-Only header instead of Content-Security-Policy when true. Defaults to true.
• directives : A collection of valid CSP directives provided as key/value pairs. The key must be a lowercase String and must be comprised of the characters [a-z] and the -. The value must also be a String but is not limited to remain flexible as the CSP standards evolve. You can use conditional statements within the configuration block to set values dynamically at startup time. Defaults to an empty config that you must configure. An empty config will raise an exception.

Note that certain CSP directives, such as upgrade-insecure-requests, do not take any arguments. For those, just set the value to true.

Learn more about the Content Security Policy at the following sites:

• W3C CSP Level 1 (deprecated) : https://www.w3.org/TR/CSP1/
• W3C CSP Level 2 (current) : https://www.w3.org/TR/CSP2/
• W3C CSP Level 3 (draft) : https://www.w3.org/TR/CSP3/
• https://developer.mozilla.org/en-US/docs/Web/Security/CSP
• http://caniuse.com/#search=ContentSecurityPolicy
• http://content-security-policy.com/
• https://securityheaders.io
• https://scotthelme.co.uk/csp-cheat-sheet/
• http://www.html5rocks.com/en/tutorials/security/content-security-policy/
• https://hacks.mozilla.org/2016/02/implementing-content-security-policy/

require 'rack/content_security_policy'

Rack::ContentSecurityPolicy.configure do |d|
  d.report_only = false
  d['default-src'] = "'none'"
  d['script-src']  = "'self'"
  d['upgrade-insecure-requests'] = true
end

use Rack::ContentSecurityPolicy

require 'rack/content_security_policy'

use Rack::ContentSecurityPolicy, report_only: true, directives: { 'default-src' => "'self'" }

After checking out the repo, run bundle install to install dependencies. Then, run bundle exec rake to run the specs.

To install this gem onto your local machine, run bundle exec rake install.

This gem is cryptographically signed. To be sure the gem you install hasn’t been tampered with you can install it using the following method:

Add my public key (if you haven’t already) as a trusted certificate

# Caveat: Gem certificates are trusted globally, such that adding a
# cert.pem for one gem automatically trusts all gems signed by that cert.
gem cert --add <(curl -Ls https://raw.github.com/grempe/rack-content_security_policy/master/certs/gem-public_cert_grempe_2026.pem)

To install, it is possible to specify either HighSecurity or MediumSecurity mode. Since this gem depends on one or more gems that are not cryptographically signed you will likely need to use MediumSecurity. You should receive a warning if any signed gem does not match its signature.

# All signed dependent gems must be verified.
gem install rack-content_security_policy -P MediumSecurity

You can learn more about security and signed Ruby Gems.

Most, if not all, of the commits and tags to this repository are signed with my PGP/GPG code signing key. I have uploaded my code signing public keys to GitHub and you can now verify those signatures with the GitHub UI. See this list of commits and look for the Verified tag next to each commit. You can click on that tag for additional information.

You can also clone the repository and verify the signatures locally using your own GnuPG installation. You can find my certificates and read about how to conduct this verification at https://www.rempe.us/keys/.

Bug reports and pull requests are welcome on GitHub at https://github.com/grempe/rack-content_security_policy. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

Copyright (c) 2016 Glenn Rempe <glenn@rempe.us> (https://www.rempe.us/)

Some portions Copyright (c) 2009-2012 Alexey Rodionov

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

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the LICENSE.txt file for the specific language governing permissions and limitations under the License.

Thanks to Alexey Rodionov (@p0deje) for his well written original implementation of CSP.