sinatra/rack-protection/lib/rack/protection/content_security_policy.rb

# -*- coding: utf-8 -*-
require 'rack/protection'

module Rack
  module Protection
    ##
    # Prevented attack::   XSS and others
    # Supported browsers:: Firefox 23+, Safari 7+, Chrome 25+, Opera 15+
    #
    # Description:: Content Security Policy, a mechanism web applications
    #               can use to mitigate a broad class of content injection
    #               vulnerabilities, such as cross-site scripting (XSS).
    #               Content Security Policy is a declarative policy that lets
    #               the authors (or server administrators) of a web application
    #               inform the client about the sources from which the
    #               application expects to load resources.
    #
    # More info::   W3C CSP Level 1 : https://www.w3.org/TR/CSP1/ (deprecated)
    #               W3C CSP Level 2 : https://www.w3.org/TR/CSP2/ (current)
    #               W3C CSP Level 3 : https://www.w3.org/TR/CSP3/ (draft)
    #               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/
    #
    # Sets the 'Content-Security-Policy[-Report-Only]' header.
    #
    # Options: ContentSecurityPolicy configuration is a complex topic with
    #          several levels of support that has evolved over time.
    #          See the W3C documentation and the links in the more info
    #          section for CSP usage examples and best practices. The
    #          CSP3 directives in the 'NO_ARG_DIRECTIVES' constant need to be
    #          presented in the options hash with a boolean 'true' in order
    #          to be used in a policy.
    #
    class ContentSecurityPolicy < Base
      default_options default_src: "'self'", report_only: false

      DIRECTIVES = %i(base_uri child_src connect_src default_src
                      font_src form_action frame_ancestors frame_src
                      img_src manifest_src media_src object_src
                      plugin_types referrer reflected_xss report_to
                      report_uri require_sri_for sandbox script_src
                      style_src worker_src webrtc_src navigate_to
                      prefetch_src).freeze

      NO_ARG_DIRECTIVES = %i(block_all_mixed_content disown_opener
                             upgrade_insecure_requests).freeze

      def csp_policy
        directives = []

        DIRECTIVES.each do |d|
          if options.key?(d)
            directives << "#{d.to_s.sub(/_/, '-')} #{options[d]}"
          end
        end

        # Set these key values to boolean 'true' to include in policy
        NO_ARG_DIRECTIVES.each do |d|
          if options.key?(d) && options[d].is_a?(TrueClass)
            directives << d.to_s.tr('_', '-')
          end
        end

        directives.compact.sort.join('; ')
      end

      def call(env)
        status, headers, body = @app.call(env)
        header = options[:report_only] ? 'Content-Security-Policy-Report-Only' : 'Content-Security-Policy'
        headers[header] ||= csp_policy if html? headers
        [status, headers, body]
      end
    end
  end
end