Trust X-Forwarded-For from the right to the left #162
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In modosc#149 we got the extremely helpful `Request#cloudflare?` method which can assist with checking if a request has been proxied through Cloudflare. The method checks that there's an unbroken chain of trust from the `REMOTE_ADDR` (if it exists) through forwarded IPs that only includes trusted internal proxies and Cloudflare IP addresses. Each proxy in the chain is supposed to append the IP of the traffic it received to the *right side* of `X-Forwarded-For`. This means that after evaluating `REMOTE_ADDR` we should be looking at addresses in `X-Forwarded-For` starting on the right side, not on the left. https://github.com/modosc/cloudflare-rails/blob/311875eef57862ecf050fb87415c56ea4823486a/lib/cloudflare_rails/check_trusted_proxies.rb#L23-L25 This ordering means that if a request has the original client as the first address in `X-Forwarded-For` that we'll incorrectly reject it. It also means that an attacker could craft a forged `X-Forwarded-For` that starts with a Cloudflare IP and smuggle in a request that appears to be valid to the method's logic. The fix here is to continue to look at `REMOTE_ADDR` first but then to look at `X-Forwarded-For` in right-to-left order until we run out of trusted IP addresses (whether internal proxies or Cloudflare IPs). Fix modosc#161
geoffharcourt
commented
Oct 4, 2024
| ```ruby | ||
| config.cloudflare.expires_in = 12.hours # default value | ||
| config.cloudflare.timeout = 5.seconds # default value | ||
| ``` | ||
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| ## Blocking non-Cloudflare traffic | ||
| You can use the `#cloudfront?` method from this gem to block all non-Cloudflare traffic to your application. Here's an example of doing this with [`Rack::Attack`](https://github.com/rack/rack-attack): | ||
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| You can use the `#cloudflare?` method from this gem to block all non-Cloudflare traffic to your application. Here's an example of doing this with [`Rack::Attack`](https://github.com/rack/rack-attack): |
geoffharcourt
commented
Oct 4, 2024
| - `REMOTE_ADDR: CloudFlare` | ||
| - `REMOTE_ADDR: trusted_proxy`, `X_HTTP_FORWARDED_FOR: CloudFlare` | ||
| - `REMOTE_ADDR: trusted_proxy`, `X_HTTP_FORWARDED_FOR: CloudFlare,trusted_proxy2` | ||
| - `REMOTE_ADDR: trusted_proxy`, `X_HTTP_FORWARDED_FOR: untrusted,CloudFlare` |
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Updated to show the expectations.
geoffharcourt
commented
Oct 4, 2024
| @@ -139,11 +144,6 @@ | |||
| it 'returns false if the request has a trusted REMOTE_ADDR but did not originate from CloudFlare' do | |||
| expect(Rack::Request.new('REMOTE_ADDR' => '10.1.1.1', 'HTTP_X_FORWARDED_FOR' => '1.2.3.4')).not_to be_cloudflare | |||
| end | |||
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| it 'returns false if the request has a trusted REMOTE_ADDR and an untrusted proxy before CloudFlare' do | |||
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This spec should be true, moved it up and reworded.
geoffharcourt
commented
Oct 4, 2024
| @@ -122,9 +122,14 @@ | |||
| 'HTTP_X_FORWARDED_FOR' => '10.2.2.2,197.234.240.1')).to be_cloudflare | |||
| end | |||
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| it 'returns true if the request originated from CloudFlare via one trusted proxy and one untrusted upstream IP' do | |||
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This spec should be false, reworded and moved it down.
modosc
approved these changes
Oct 7, 2024
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Thanks for the quick review and merge @modosc! |
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In #149 we got the extremely helpful
Request#cloudflare?method which can assist with checking if a request has been proxied through Cloudflare. The method checks that there's an unbroken chain of trust from theREMOTE_ADDR(if it exists) through forwarded IPs that only includes trusted internal proxies and Cloudflare IP addresses.Each proxy in the chain is supposed to append the IP of the traffic it received to the right side of
X-Forwarded-For. This means that after evaluatingREMOTE_ADDRwe should be looking at addresses inX-Forwarded-Forstarting on the right side, not on the left.cloudflare-rails/lib/cloudflare_rails/check_trusted_proxies.rb
Lines 23 to 25 in 311875e
This ordering means that if a request has the original client as the first address in
X-Forwarded-Forthat we'll incorrectly reject it. It also means that an attacker could craft a forgedX-Forwarded-Forthat starts with a Cloudflare IP and smuggle in a request that appears to be valid to the method's logic.The fix here is to continue to look at
REMOTE_ADDRfirst but then to look atX-Forwarded-Forin right-to-left order until we run out of trusted IP addresses (whether internal proxies or Cloudflare IPs).Fix #161