Rack::Cloudflare

Deal with Cloudflare features in your Ruby app using Rack middleware. Also provides a Ruby toolkit to deal with Cloudflare in other contexts if you'd like.

Installation

Add this line to your application's Gemfile:

gem 'rack-cloudflare'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rack-cloudflare

Usage

Whitelist Cloudflare IP addresses

You can block access to non-Cloudflare networks using Rack::Cloudflare::Middleware::AccessControl.

require 'rack/cloudflare'

# In config.ru (recommended for Rails as well to preempt application loading)
use Rack::Cloudflare::Middleware::AccessControl

# In Rails middleware: config/application.rb
config.middleware.unshift Rack::Cloudflare::Middleware::AccessControl

# Configure custom blocked message (defaults to "Forbidden")
Rack::Cloudflare::Middleware::AccessControl.message = "You don't belong here..."

# Fully customize the Rack response (such as making it a redirect)
Rack::Cloudflare::Middleware::AccessControl.response = lambda do |_env|
    [301, { 'Location' => 'https://somewhere.else.xyz' }, ["Redirecting...\n"]]
end

Alternatively, using Rack::Attack you can easily add a "safelist" rule.

Rack::Attack.safelist('Only allow requests through the Cloudflare network') do |request|
    Rack::Cloudflare::Headers.trusted?(request.env)
end

Utilizing the trusted? helper method, you can implement a similar check using other middleware.

See Toolkits: Detect Cloudflare Requests for alternative uses.

Rewrite Cloudflare Remote/Client IP address

You can set REMOTE_ADDR to the correct remote IP using Rack::Cloudflare::Middleware::RewriteHeaders.

require 'rack/cloudflare'

# In config.ru
use Rack::Cloudflare::Middleware::RewriteHeaders

# In Rails config/application.rb
config.middleware.use Rack::Cloudflare::Middleware::RewriteHeaders

You can customize whether rewritten headers should be backed up and what names to use.

# Toggle header backups (default: true)
Rack::Cloudflare::Headers.backup = false

# Rename backed up headers (defaults: "ORIGINAL_REMOTE_ADDR", "ORIGINAL_FORWARDED_FOR")
Rack::Cloudflare::Headers.original_remote_addr   = 'BACKUP_REMOTE_ADDR'
Rack::Cloudflare::Headers.original_forwarded_for = 'BACKUP_FORWARDED_FOR'

See Toolkits: Rewrite Headers for alternative uses.

Logging

You can enable logging to see what requests are blocked or headers are rewritten.

Rack::Cloudflare.logger = Logger.new(STDOUT)

Log levels used are INFO, DEBUG and WARN.

Toolkits

Detect Cloudflare Requests

You can very easily check your HTTP headers to see if the request came from a Cloudflare network.

# Your headers are in a `Hash` format
# e.g. { 'REMOTE_ADDR' => '0.0.0.0', ... }
# Verifies the remote address
Rack::Cloudflare::Headers.trusted?(headers)

Note that we can only trust the REMOTE_ADDR header to verify a request came from Cloudflare. The HTTP_X_FORWARDED_FOR header can be modified and therefore not trusted.

Make sure your web server does not modify REMOTE_ADDR because it could cause security holes. Read this article, for example: Anatomy of an Attack: How I Hacked StackOverflow

Rewrite Headers

We can easily rewrite REMOTE_ADDR and add HTTP_X_FORWARDED_FOR based on verifying the request comes from a Cloudflare network.

# Get a list of headers relevant to Cloudflare (unmodified)
headers = Rack::Cloudflare::Headers.new(headers).target_headers

# Get a list of headers that will be rewritten (modified)
headers = Rack::Cloudflare::Headers.new(headers).rewritten_headers

# Get a list of headers relevant to Cloudflare with rewritten values
headers = Rack::Cloudflare::Headers.new(headers).rewritten_target_headers

# Update original headers with rewritten ones
headers = Rack::Cloudflare::Headers.new(headers).rewrite

Up-to-date Cloudflare IP addresses

Cloudflare provides a list of IP addresses that are important to keep up-to-date.

A copy of the IPs are kept in /data. The list is converted to a IPAddr list and is accessible as:

# Configurable list of IPs
# Defaults to Rack::Cloudflare::IPs::DEFAULTS
Rack::Cloudflare::IPs.list

The list can be updated to Cloudflare's latest published IP lists in-memory:

# Fetches Rack::Cloudflare::IPs::V4_URL and Rack::Cloudflare::IPs::V6_URL
Rack::Cloudflare::IPs.update!

# Updates cached list in-memory
Rack::Cloudflare::IPs.list

Credits

Inspired by:

• https://github.com/tatey/rack-cloudflare
• https://github.com/rikas/cloudflare_localizable

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/joelvh/rack-cloudflare.