Optionally allow ActionCable requests from the same host as origin #26568

merged 1 commit into from Oct 11, 2016


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When the allow_same_origin_as_host is set to true, the request
forgery protection permits HTTP_ORIGIN values starting with the
corresponding proto:// prefix followed by HTTP_HOST. This way
it is not required to specify the list of allowed URLs.

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FYI @matthewd

@skateman skateman referenced this pull request in ManageIQ/manageiq Sep 21, 2016

Enable the previously disabled ActionCable #11396


I think we can enable this always, without needing a config option.

The point of the origin check is to protect against cross-origin websocket connections, which could give privileged access because of a cookie; if the origin matches the request hostname, then the originating page already had access to any such cookie... right?

cc @rails/security

if Array(server.config.allowed_request_origins).any? { |allowed_origin| allowed_origin === env["HTTP_ORIGIN"] }
+ elsif server.config.allow_same_origin_as_host && env["HTTP_ORIGIN"].start_with?("#{proto}://#{env['HTTP_HOST']}")
matthewd Sep 21, 2016 Member

Origin doesn't have a suffix, so this should be an == comparison.

@matthewd matthewd assigned matthewd and unassigned rafaelfranca Sep 21, 2016
+ @server.config.allow_same_origin_as_host = true
+ assert_origin_allowed "http://#{HOST}"
+ assert_origin_not_allowed "http://hax.com"
+ assert_origin_not_allowed "http://rails.co.uk/"
matthewd Sep 21, 2016 Member

I think the allowed one should be a literal string.. probably. And this last line needs to lose the trailing / to have much meaning.

Also, is this test leaving the config option set? The teardown makes sure to reset the others.

skateman Sep 21, 2016 Contributor

@matthewd both fixed

@skateman skateman Optionally allow ActionCable requests from the same host as origin
When the `allow_same_origin_as_host` is set to `true`, the request
forgery protection permits `HTTP_ORIGIN` values starting with the
corresponding `proto://` prefix followed by `HTTP_HOST`. This way
it is not required to specify the list of allowed URLs.
jeremy commented Sep 21, 2016

if the origin matches the request hostname

That protects against same-origin cookies (barring DNS rebinding which would poke through in any case) conferring auth, but not against accepting the connection in the first place, affecting apps with non-authenticated conns and (marginally) increasing DoS risk.


Even DNS rebinding is okay, because that only gets the attacker access to cookies belonging to their rebound name, not the "real" one.

If the code making the request came from the same origin as the hostname you've been supplied (here, a DNS rebinding disclaimer is indeed required), then regardless of whether the hostname is the real one or an attacker-owned fake pointing at your IP, it's your code.

AIUI, the only real exposure here is if the connection-initiating-party can fake one or both of those headers (giving a host header that didn't resolve to this server, or an origin that isn't true)... and at that point, you're dealing with something other than a browser, which would be just as capable of claiming whatever origin you're explicitly checking for.

@matthewd matthewd merged commit 268c340 into rails:master Oct 11, 2016

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Defaulted to on in dae4044; I decided to stop short of removing the option altogether.

@skateman skateman deleted the skateman:cable-sameorigin-as-host branch Oct 11, 2016
matthewd commented Oct 11, 2016 edited

Backported to 5-0-stable: db70978 + 549d732

@matthewd matthewd referenced this pull request Oct 11, 2016
@matthewd matthewd Permit same-origin connections by default
WebSocket always defers the decision to the server, because it didn't
have to deal with legacy compatibility... but the same-origin policy is
still a reasonable default.

Origin checks do not protect against a directly connecting attacker --
they can lie about their host, but can also lie about their origin.
Origin checks protect against a connection from 3rd-party controlled
script in a context where a victim browser's cookies will be passed
along. And if an attacker has breached that protection, they've already
compromised the HTTP session, so treating the WebSocket connection in
the same way seems reasonable.

In case this logic proves incorrect (or anyone just wants to be more
paranoid), we retain a config option to disable it.
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