[OpenID] Abusing Authentication Failure messages

[Maarten Billemont]

On 20 Aug 2010, at 16:17, Andrew Arnott wrote:

> I don't consider this a flaw at all.  In fact you can solve it yourself today, in total compliance with the OpenID spec.  
> 
> Use the return_to parameter to add whatever unique ID you wish was there.  Then in your logs, you'll see the ID on the outgoing request (if you log it) and on the response (via the incoming HTTP indirect message).  
> 
> Problem solved, right?  It's totally up to the RP (you) to leverage this hidden "feature" of ways to use return_to.

Might I ask what the wisdom behind this is?

I have the feeling OpenID is all about a way of authenticating users and exchanging identity information but utter minimal requirements to do that in a secure fashion.  All features that are there to protect against known and proven attack vectors are optional.  And as indicated by this thread, some attack vectors aren't even dealt with by the protocol: one would need to do silly undocumented stuff to existing parameters or add extensions to the protocol.  You could say, the OpenID protocol is the exact opposite of "Secure By Default".  And designing a protocol that way only encourages lazy implementations that have no regard for user privacy concerns.

Do the OpenID designers hold security in a low regard or does security come second to "ease of implementation" (frankly, a secure protocol is just as easily adopted given good reference implementations).  Perhaps I'm not seeing all the reasons why OpenID was designed the way it was - can anyone shed some light?

> 
> In particular, DotNetOpenAuth utilizes return_to when its optional feature is activated that disables "unsolicited assertions", which guarantees that each authentication response starts with an authentication request that originated at the RP.  We had a signed nonce from the RP to the return_to, and verify it when it comes back.  Again, this is only if you wanted to disable unsolicited assertions deliberately for some reason.
> 
> --
> Andrew Arnott
> "I [may] not agree with what you have to say, but I'll defend to the death your right to say it." - S. G. Tallentyre
> 
> 
> On Fri, Aug 20, 2010 at 2:12 AM, Maarten Billemont <lhunath at gmail.com> wrote:
> It has always bothered me that the OpenID protocol does not assign a unique ID to requests that is required to be repeated in the request's response.  This makes it annoying to cleanly identify whether a response matches a particular request; instead relying on chronology (response Y comes after request X?  It must be a response to X!).
> 
> This is an annoyance, yet, in the case of successful authentication responses, not a disaster: The response can be signed and verified.
> 
> In the case of a failure response, however, there is a significant lack of useful information passed from the OP to the RP.  This lack of useful information makes it impossible for the RP to verify that the response did originate from the OP.  Unfortunately for the RP, (and conveniently for an attacker), the response is sent via indirect communication (via the User Agent); so the RP has no clue whatsoever where the response came from or who crafted it.  There is no association handle, no signature, no nonce, no nothing.
> 
> Does that mean that to sabotage an OpenID site's authentication process, all I have to do is craft a website which, when opened by the user in a separate tab, continuously makes requests to the RP providing authentication failure responses?
> 
> Am I missing something here, or is the OpenID protocol really so flawed?  And if it is, can I expect anyone to fix the protocol any time soon?
> 
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