Cookie settings and CSP hash sources

3.2.0 Cookie settings and CSP hash sources

Cookies

SecureHeaders supports Secure, HttpOnly and SameSite cookies. These can be defined in the form of a boolean, or as a Hash for more refined configuration.

Note: Regardless of the configuration specified, Secure cookies are only enabled for HTTPS requests.

Boolean-based configuration

Boolean-based configuration is intended to globally enable or disable a specific cookie attribute.

config.cookies = {
  secure: true, # mark all cookies as Secure
  httponly: false, # do not mark any cookies as HttpOnly
}

Hash-based configuration

Hash-based configuration allows for fine-grained control.

config.cookies = {
  secure: { except: ['_guest'] }, # mark all but the `_guest` cookie as Secure
  httponly: { only: ['_rails_session'] }, # only mark the `_rails_session` cookie as HttpOnly
}

SameSite cookie configuration

SameSite cookies permit either Strict or Lax enforcement mode options.

config.cookies = {
  samesite: {
    strict: true # mark all cookies as SameSite=Strict
  }
}

Strict and Lax enforcement modes can also be specified using a Hash.

config.cookies = {
  samesite: {
    strict: { only: ['_rails_session'] },
    lax: { only: ['_guest'] }
  }
}

Hash

script/style-src hashes can be used to whitelist inline content that is static. This has the benefit of allowing inline content without opening up the possibility of dynamic javascript like you would with a nonce.

You can add hash sources directly to your policy :

::SecureHeaders::Configuration.default do |config|
   config.csp = {
     default_src: %w('self')

     # this is a made up value but browsers will show the expected hash in the console.
     script_src: %w(sha256-123456)
   }
 end

You can also use the automated inline script detection/collection/computation of hash source values in your app.

 rake secure_headers:generate_hashes

This will generate a file (config/config/secure_headers_generated_hashes.yml by default, you can override by setting ENV["secure_headers_generated_hashes_file"]) containing a mapping of file names with the array of hash values found on that page. When ActionView renders a given file, we check if there are any known hashes for that given file. If so, they are added as values to the header.

---
scripts:
  app/views/asdfs/index.html.erb:
  - "'sha256-yktKiAsZWmc8WpOyhnmhQoDf9G2dAZvuBBC+V0LGQhg='"
styles:
  app/views/asdfs/index.html.erb:
  - "'sha256-SLp6LO3rrKDJwsG9uJUxZapb4Wp2Zhj6Bu3l+d9rnAY='"
  - "'sha256-HSGHqlRoKmHAGTAJ2Rq0piXX4CnEbOl1ArNd6ejp2TE='"

Helpers

This will not compute dynamic hashes by design. The output of both helpers will be a plain script/style tag without modification and the known hashes for a given file will be added to script-src/style-src when hashed_javascript_tag and hashed_style_tag are used. You can use raise_error_on_unrecognized_hash = true to be extra paranoid that you have precomputed hash values for all of your inline content. By default, this will raise an error in non-production environments.

<%= hashed_style_tag do %>
body {
  background-color: black;
}
<% end %>

<%= hashed_style_tag do %>
body {
  font-size: 30px;
  font-color: green;
}
<% end %>

<%= hashed_javascript_tag do %>
console.log(1)
<% end %>

Content-Security-Policy: ...
 script-src 'sha256-yktKiAsZWmc8WpOyhnmhQoDf9G2dAZvuBBC+V0LGQhg=' ... ;
 style-src 'sha256-SLp6LO3rrKDJwsG9uJUxZapb4Wp2Zhj6Bu3l+d9rnAY=' 'sha256-HSGHqlRoKmHAGTAJ2Rq0piXX4CnEbOl1ArNd6ejp2TE=' ...;