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.

Automagic

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

• It adds 'chrome-extension:' to your CSP directives by default. This helps drastically reduce the amount of reports, but you can also disable this feature by supplying :disable_chrome_extension => true.
• 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.
• It copies the connect-src value to xhr-src for AJAX requests.
• 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 (the forward_endpoint value or 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 :report_uri without restriction. More information can be found in the "Note on Firefox handling of CSP" section.

Configuration

Place the following in an initializer:

::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",
    # ALWAYS supply a full URL for report URIs
    :report_uri => 'https://example.com/uri-directive',
    :img_src => "https://* data:",
    :frame_src => "https://* http://*.twimg.com http://itunes.apple.com"
  }
end

# and then simply include
ensure_security_headers

Or simply add it to application controller

ensure_security_headers
  :hsts => {:include_subdomains, :x_frame_options => false},
  :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.

Widely supported

:hsts             => {:max_age => 631138519, :include_subdomain => true}
:x_frame_options  => {:value => 'SAMEORIGIN'}
:x_xss_protection => {:value => '1', :mode => false}  # set the :mode option to 'block' to enforce the browser's xss filter

Content Security Policy (CSP)

All browsers will receive the webkit csp header except Firefox, which gets its own header. See WebKit/W3C specification and Firefox 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 full URLs.
  :report_uri  => 'https://mylogaggregator.example.com',

  # Send reports that cannot be sent across host here (see below), forward them to report_uri
  # override this if you have a route with the same value (content_security_policy#scribe)
  :forward_endpoint => SecureHeaders::ContentSecurityPolicy::FF_CSP_ENDPOINT

  # 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'
    }
  }
}

Only applied to IE

:x_content_type_options => {:value => 'nosniff'}

Example CSP header config

Configure the CSP header as if it were the w3c-style header, no need to supply 'options' or 'allow' directives.

# most basic example
:csp => {
  :default_src => "https://* inline eval",
  :report_uri => '/uri-directive'
}
# Chrome
> "default-src 'unsafe-inline' 'unsafe-eval' https://* chrome-extension:; report-uri /uri-directive;"
# Firefox
> "options inline-script eval-script; allow https://*; report-uri /uri-directive;"

# turn off inline scripting/eval
:csp => {
  :default_src => 'https://*',
  :report_uri => '/uri-directive'
}
# Chrome
> "default-src  https://*; report-uri /uri-directive;"
# Firefox
> "allow 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'
}
# Chrome
"default-src  'self'; img-src *; object-src media1.com media2.com *.cdn.com; script-src trustedscripts.example.com;"
# Firefox
"allow 'self'; img-src *; object-src media1.com media2.com *.cdn.com; script-src trustedscripts.example.com;"

Note on Firefox handling of CSP

Currently, Firefox does not support the w3c draft standard. So there are a few steps taken to make the two interchangeable.

Firefox > 18 partially supports the standard via using the default-src directive over allow/options, but the following inconsistencies remain.

• inline-script or eval-script values in default/style/script-src directives are moved to the options directive. Note: the style-src directive is not fully supported in Firefox - see https://bugzilla.mozilla.org/show_bug.cgi?id=763879.
• 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.
• Firefox adds port numbers to each /https?/ value which can make local development tricky with mocked services. Add environment specific code to configure this.

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!!!

If you need to change the route for the internal forwarding point, be sure it matches what is set in :forward_endpoint or else the reports will post to a non-existent endpoint.

Rails 2

map.csp_endpoint

Rails 3

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

match 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",
    # ALWAYS supply a full URL for report URIs
    :report_uri => 'https://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(request, nil)
    haml :index
  end
end

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 Firefox 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 Twitter, Inc.

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