SecureHeaders

The gem will automatically apply several headers that are related to security. This includes:

• Content Security Policy (CSP) - Helps detect/prevent XSS, mixed-content, and other classes of attack. CSP 1.1 Specification
• HTTP Strict Transport Security (HSTS) - Ensures the browser never visits the http version of a website. Protects from SSLStrip/Firesheep attacks. HSTS Specification
• X-Frame-Options (XFO) - Prevents your content from being framed and potentially clickjacked. X-Frame-Options draft
• X-XSS-Protection - Cross site scripting heuristic filter for IE/Chrome
• X-Content-Type-Options - Prevent content type sniffing

This gem has integration with Rails, but works for any Ruby code. See the sinatra example section.

Installation

Add to your Gemfile

gem 'secure_headers'

And then execute:

$ bundle

Or install it yourself as:

$ gem install secure_headers

Usage

Functionality provided

• ensure_security_headers: will set security-related headers automatically based on the configuration below.

By default, it will set all of the headers listed in the options section below unless specified.

Disabling

Use the standard skip_before_filter :filter_name, options mechanism. e.g. skip_before_filter :set_csp_header, :only => :tinymce_page

The following methods are going to be called, unless they are provided in a skip_before_filter block.

• :set_csp_header
• :set_hsts_header
• :set_x_frame_options_header
• :set_x_xss_protection_header
• :set_x_content_type_options_header

Bonus Features

This gem makes a few assumptions about how you will use some features. For example:

• It fills any blank directives with the value in :default_src Getting a default-src report is pretty useless. This way, you will always know what type of violation occurred. You can disable this feature by supplying :disable_fill_missing => true. This is referred to as the "effective-directive" in the spec, but is not well supported as of Nov 5, 2013.
• Firefox does not support cross-origin CSP reports. If we are using Firefox, AND the value for :report_uri does not satisfy the same-origin requirements, we will instead forward to an internal endpoint (FF_CSP_ENDPOINT). This is also the case if :report_uri only contains a path, which we assume will be cross host. This endpoint will in turn forward the request to the value in :forward_endpoint without restriction. More information can be found in the "Note on Firefox handling of CSP" section.

Configuration

Place the following in an initializer (recommended):

::SecureHeaders::Configuration.configure do |config|
  config.hsts = {:max_age => 20.years.to_i, :include_subdomains => true}
  config.x_frame_options = 'DENY'
  config.x_content_type_options = "nosniff"
  config.x_xss_protection = {:value => 1, :mode => 'block'}
  config.csp = {
    :default_src => "https://* self",
    :frame_src => "https://* http://*.twimg.com http://itunes.apple.com",
    :img_src => "https://*",
    :report_uri => '//example.com/uri-directive'
  }
end

# and then simply include this in application_controller.rb
class ApplicationController < ActionController::Base
  ensure_security_headers
end

Or simply add it to application controller

ensure_security_headers(
  :hsts => {:include_subdomains => true, :max_age => 20.years.to_i},
  :x_frame_options => 'DENY',
  :csp => false
)

Options for ensure_security_headers

To disable any of these headers, supply a value of false (e.g. :hsts => false), supplying nil will set the default value

Each header configuration can take a hash, or a string, or both. If a string is provided, that value is inserted verbatim. If a hash is supplied, a header will be constructed using the supplied options.

The Easy Headers

This configuration will likely work for most applications without modification.

:hsts             => {:max_age => 631138519, :include_subdomains => false}
:x_frame_options  => {:value => 'SAMEORIGIN'}
:x_xss_protection => {:value => 1, :mode => 'block'}  # set the :mode option to false to use "warning only" mode
:x_content_type_options => {:value => 'nosniff'}

Content Security Policy (CSP)

All browsers will receive the webkit csp header except Firefox, which gets its own header. See WebKit specification and Mozilla CSP specification

:csp => {
  :enforce     => false,        # sets header to report-only, by default
  # default_src is required!
  :default_src     => nil,      # sets the default-src/allow+options directives

  # Where reports are sent. Use protocol relative URLs if you are posting to the same domain (TLD+1). Use paths if you are posting to the application serving the header
  :report_uri  => '//mysite.example.com',

  # Send reports that cannot be sent across host here. These requests are sent
  # the server, not the browser. If no value is supplied, it will default to
  # the value in report_uri. Use this if you cannot use relative protocols mentioned above due to host mismatches.
  :forward_endpoint => 'https://internal.mylogaggregator.example.com'

  # these directives all take 'none', 'self', or a globbed pattern
  :img_src     => nil,
  :frame_src   => nil,
  :connect_src => nil,
  :font_src    => nil,
  :media_src   => nil,
  :object_src  => nil,
  :style_src   => nil,
  :script_src  => nil,

  # http additions will be appended to the various directives when
  # over http, relaxing the policy
  # e.g.
  # :csp => {
  #   :img_src => 'https://*',
  #   :http_additions => {:img_src => 'http//*'}
  # }
  # would produce the directive: "img-src https://* http://*;"
  # when over http, ignored for https requests
  :http_additions => {}

  # If you have enforce => true, you can use the `experiments` block to
  # also produce a report-only header. Values in this block override the
  # parent config for the report-only, and leave the enforcing header
  # unaltered. http_additions work the same way described above, but
  # are added to your report-only header as expected.
  :experimental => {
    :script_src => 'self',
    :img_src => 'https://mycdn.example.com',
    :http_additions {
      :img_src => 'http://mycdn.example.com'
    }
  }
}

Example CSP header config

# most basic example
:csp => {
  :default_src => "https://* inline eval",
  :report_uri => '/uri-directive'
}

> "default-src 'unsafe-inline' 'unsafe-eval' https://*; report-uri /uri-directive;"

# turn off inline scripting/eval
:csp => {
  :default_src => 'https://*',
  :report_uri => '/uri-directive'
}

> "default-src  https://*; report-uri /uri-directive;"

# Auction site wants to allow images from anywhere, plugin content from a list of trusted media providers (including a content distribution network), and scripts only from its server hosting sanitized JavaScript
:csp => {
  :default_src => 'self',
  :img_src => '*',
  :object_src => ['media1.com', 'media2.com', '*.cdn.com'],
  # alternatively (NOT csv) :object_src => 'media1.com media2.com *.cdn.com'
  :script_src => 'trustedscripts.example.com'
}
"default-src  'self'; img-src *; object-src media1.com media2.com *.cdn.com; script-src trustedscripts.example.com;"

Tagging Requests

It's often valuable to send extra information in the report uri that is not available in the reports themselves. Namely, "was the policy enforced" and "where did the report come from"

{
  :tag_report_uri => true,
  :enforce => true,
  :app_name => 'twitter',
  :report_uri => 'csp_reports'
}

Results in

report-uri csp_reports?enforce=true&app_name=twitter

CSP Level 2 features

script/style-nonce can be used to whitelist inline content. To do this, add "nonce" to your script/style-src configuration, then set the nonce attributes on the various tags.

*setting a nonce will also set 'unsafe-inline' for browsers that don't support nonces for backwards compatibility. 'unsafe-inline' is ignored if a nonce is present in a directive in compliant browsers.

:csp => {
  :default_src => 'self',
  :script_src => 'self nonce'
}

content-security-policy: default-src 'self'; script-src 'self' 'nonce-abc123' 'unsafe-inline'

<script nonce="<%= @content_security_policy_nonce %>">
  console.log("whitelisted, will execute")
</script>

<script nonce="lol">
  console.log("won't execute, not whitelisted")
</script>

<script>
  console.log("won't execute, not whitelisted")
</script>

Note on Firefox handling of CSP

• CSP reports will not POST cross-origin. This sets up an internal endpoint in the application that will forward the request. Set the forward_endpoint value in the CSP section if you need to post cross origin for firefox. The internal endpoint that receives the initial request will forward the request to forward_endpoint

Adding the Firefox report forwarding endpoint

You need to add the following line to the TOP of confib/routes.rb This is an unauthenticated, unauthorized endpoint. Only do this if your report-uri is not on the same origin as your application!!!

Rails 2

map.csp_endpoint

Rails 3

If the csp reporting endpoint is clobbered by another route, add:

post SecureHeaders::ContentSecurityPolicy::FF_CSP_ENDPOINT => "content_security_policy#scribe"

Using with Sinatra

Here's an example using SecureHeaders for Sinatra applications:

require 'rubygems'
require 'sinatra'
require 'haml'
require 'secure_headers'

::SecureHeaders::Configuration.configure do |config|
  config.hsts = {:max_age => 99, :include_subdomains => true}
  config.x_frame_options = 'DENY'
  config.x_content_type_options = "nosniff"
  config.x_xss_protection = {:value => 1, :mode => false}
  config.csp = {
    :default_src => "https://* inline eval",
    :report_uri => '//example.com/uri-directive',
    :img_src => "https://* data:",
    :frame_src => "https://* http://*.twimg.com http://itunes.apple.com"
  }
end

class Donkey < Sinatra::Application
  include SecureHeaders
  set :root, APP_ROOT

  get '/' do
    set_csp_header
    haml :index
  end
end

Using with Padrino

You can use SecureHeaders for Padrino applications as well:

In your Gemfile:

  gem "secure_headers", :require => 'secure_headers'

then in your app.rb file you can:

require 'secure_headers/padrino'

module Web
  class App < Padrino::Application
    register SecureHeaders::Padrino

    get '/' do
      set_csp_header
      render 'index'
    end
  end
end

and in config/boot.rb:

def before_load
  ::SecureHeaders::Configuration.configure do |config|
    config.hsts                   = {:max_age => 99, :include_subdomains => true}
    config.x_frame_options        = 'DENY'
    config.x_content_type_options = "nosniff"
    config.x_xss_protection       = {:value   => '1', :mode => false}
    config.csp                    = {
      :default_src => "https://* inline eval",
      :report_uri => '//example.com/uri-directive',
      :img_src => "https://* data:",
      :frame_src => "https://* http://*.twimg.com http://itunes.apple.com"
    }
  end
end

Similar libraries

• Node.js (express) helmet and hood
• J2EE Servlet >= 3.0 highlines
• ASP.NET - NWebsec
• Python - django-csp + commonware
• Go - secureheader

Authors

• Neil Matatall @ndm - primary author.
• Nicholas Green @nickgreen - code contributions, main reviewer.

Acknowledgements

• Justin Collins @presidentbeef & Jim O'Leary @jimio for reviews.
• Ian Melven @imelven - Discussions/info about CSP in general, made us aware of the userCSP Mozilla extension.
• Sumit Shah @omnidactyl - For being an eager guinea pig.
• Chris Aniszczyk @cra - For running an awesome open source program at Twitter.

License

Copyright 2013-2014 Twitter, Inc and other contributors.

Licensed under the Apache License, Version 2.0: http://www.apache.org/licenses/LICENSE-2.0