Posted 14 days ago. Visible to the public.

Rails: Flagging all cookies as secure-only to pass a security audit

Why secure-only cookies used to be necessary

Cookies have an optional secure flag. It tells the browser to not send the cookie for a non-https request.

It used to be important to activate the secure flag even on sites that automatically redirect users from http:// to https://. The reason was that most users will only enter a scheme-less domain like into their location bar, which will default to in any browser. Even though the site will immediately redirect to, cookies from a prior visit will already have appeared on the unencrypted wire during the first request to

Why secure-only cookies are no longer necessary

Today, all sites should use https://. They should also set a HSTS header which makes browsers default to https:// instead of http:// when the user enters a scheme-less domain into their browser's URL bar.

For a page that exclusively uses https:// with HSTS, it is not necessary to set the secure flag on your cookies. There is simply no case when the browser would talk to the server via unencrypted http:// requests.

Why you might need secure-only cookies anyway

A security audit will still raise missing "secure" flags as an issue that needs to be fixed.

It's usually easier flag all your cookies as secure-only, than it is to explain why your application does not need secure cookies.

Rails: Automatically flag all cookies as secure-only

In a Ruby on Rails app you can add a middleware that automatically sets the Secure flag to all server-set cookies. The flag is only added for secure requests, so cookies will still work for local development where you might still use http://.

If you set any cookies from JavaScript, this isn't fixed by the middleware.

Add this to lib/middleware/secure_cookies.rb:

# On HTTPS requests, we flag all cookies sent by the application to be "Secure". # module Middleware class SecureCookies COOKIE_SEPARATOR = "\n".freeze def initialize(app) @app = app end def call(env) status, headers, body = if headers['Set-Cookie'].present? && cookies = headers['Set-Cookie'].split(COOKIE_SEPARATOR) cookies.each do |cookie| next if cookie.blank? next if cookie =~ /;\s*secure/i cookie << '; Secure' end headers['Set-Cookie'] = cookies.join(COOKIE_SEPARATOR) end [status, headers, body] end end end

Add this to your Middleware stack in the middle of config/application.rb:

require 'middleware/secure_cookies' config.middleware.insert_after ActionDispatch::Static, Middleware::SecureCookies

Add a test to spec/requests/secure_cookies_spec.rb:

describe Middleware::SecureCookies do it 'flags all cookies sent by the application as secure' do get '' response.headers['Set-Cookie'].should =~ %r(test=\S+; path=/; Secure$) end it 'will not flag cookies as secure when HTTPS is not being used (in development and tests)' do get '' response.headers['Set-Cookie'].should include('test=') # Cookie is still set response.headers['Set-Cookie'].should_not include('; Secure') end end

Note that /test/set_cookie must be an existing route that sets a cookie.

Once an application no longer requires constant development, it needs periodic maintenance for stable and secure operation. makandra offers monthly maintenance contracts that let you focus on your business while we make sure the lights stay on.

Owner of this card:

Henning Koch
Last edit:
2 days ago
by Arne Hartherz
About this deck:
We are makandra and do test-driven, agile Ruby on Rails software development.
License for source code
Posted by Henning Koch to makandra dev
This website uses cookies to improve usability and analyze traffic.
Accept or learn more