Re: [OAUTH-WG] open redirect in rfc6749

[Takahiko Kawasaki <[e-mail]>]

I think the point is that the registered redirect URI is evil, meaning that
the person who registered the client application is evil. I don't think the
spec can take any countermeasure against this case.

If the registered redirect URI is evil, the issue happens even in the case
where the scope is valid and consent from the end-user has been obtained.
That is, an attacker would prepare an HTML page at http://attacker.com
which says "Sorry, an error occurred. Please re-authorize this
application." and has a login form that mimics the login form of victim.com.

IMHO, all we can do is to educate people like "Be cautious when you are
requested to login again."

Best Regards,
Takahiko Kawasaki


2014-09-04 4:23 GMT+09:00 Phil Hunt <[e-mail]>:

> I do not believe this is a flaw specific to 6749. The flaw if any is
> within HTTP itself (RFC7230). Covert redirect is a well known problem.
> There are extensive recommendations that prevent this covered in 6749 and
> 6819.
>
> There is no protocol fix that OAuth can make since it is a trait or
> feature of HTTP.
>
> Instead we’ve made security recommendations which are the appropriate
> response to this issue. Further we published 6819 that provides further
> guidance.
>
> Phil
>
> @independentid
> www.independentid.com
> [e-mail]
>
>
>
> On Sep 3, 2014, at 11:42 AM, Hans Zandbelt <[e-mail]>
> wrote:
>
> > fine, you're talking security considerations about untrusted clients;
> that's a different use case than the protocol flaw reason why Google would
> not do rfc6749 as written
> >
> > Hans.
> >
> > On 9/3/14, 7:52 PM, John Bradley wrote:
> >> I agree that the error case where there is no UI is the problem, as it
> can be used inside a Iframe.
> >>
> >> However error responses are generally useful.
> >>
> >> OAuth core is silent on how redirect_uri are registered and if they are
> verified.
> >>
> >> Dynamic registration should warn about OAuth errors to redirect_uri
> from untrusted clients.
> >>
> >> For other registration methods we should update the RFC.
> >>
> >> John B.
> >>
> >>
> >>
> >>
> >> Sent from my iPhone
> >>
> >>> On Sep 3, 2014, at 7:14 PM, Antonio Sanso <[e-mail]> wrote:
> >>>
> >>>
> >>>> On Sep 3, 2014, at 7:10 PM, Hans Zandbelt <[e-mail]>
> wrote:
> >>>>
> >>>> Is your concern clients that were registered using dynamic client
> registration?
> >>>
> >>> yes
> >>>
> >>>>
> >>>> Otherwise the positive case is returning a response to a valid URL
> that belongs to a client that was registered explicitly by the resource
> owner
> >>>
> >>> well AFAIK the resource owner doesn’t register clients…
> >>>
> >>>
> >>>> and the negative case is returning an error to that same URL.
> >>>
> >>> the difference is the consent screen… in the positive case you need to
> approve an app.. for the error case no approval is needed,,,
> >>>
> >>>>
> >>>> I fail to see the open redirect.
> >>>
> >>> why?
> >>>
> >>>>
> >>>> Hans.
> >>>>
> >>>>> On 9/3/14, 6:56 PM, Antonio Sanso wrote:
> >>>>>
> >>>>> On Sep 3, 2014, at 6:51 PM, Hans Zandbelt <
> [e-mail]
> >>>>> <mailto:[e-mail]>> wrote:
> >>>>>
> >>>>>> Let me try and approach this from a different angle: why would you
> >>>>>> call it an open redirect when an invalid scope is provided and call
> it
> >>>>>> correct protocol behavior (hopefully) when a valid scope is
> provided?
> >>>>>
> >>>>> as specified below in the positive case (namely when the correct
> scope
> >>>>> is provided) the resource owner MUST approve the app via the consent
> >>>>> screen (at least once).
> >>>>>
> >>>>>
> >>>>>>
> >>>>>> Hans.
> >>>>>>
> >>>>>>> On 9/3/14, 6:46 PM, Antonio Sanso wrote:
> >>>>>>> hi John,
> >>>>>>> On Sep 3, 2014, at 6:14 PM, John Bradley <[e-mail]
> >>>>>>> <mailto:[e-mail]>
> >>>>>>> <mailto:[e-mail]>> wrote:
> >>>>>>>
> >>>>>>>> In the example the redirect_uri is vlid for the attacker.
> >>>>>>>>
> >>>>>>>> The issue is that the AS may be allowing client registrations with
> >>>>>>>> arbitrary redirect_uri.
> >>>>>>>>
> >>>>>>>> In the spec it is unspecified how a AS validates that a client
> >>>>>>>> controls the redirect_uri it is registering.
> >>>>>>>>
> >>>>>>>> I think that if anything it may be the registration step that
> needs
> >>>>>>>> the security consideration.
> >>>>>>>
> >>>>>>> (this is the first time :p) but I do disagree with you. It would be
> >>>>>>> pretty unpractical to block this at registration time….
> >>>>>>> IMHO the best approach is the one taken from Google, namely
> returning
> >>>>>>> 400 with the cause of the error..
> >>>>>>>
> >>>>>>> *400.* That’s an error.
> >>>>>>>
> >>>>>>> *Error: invalid_scope*
> >>>>>>>
> >>>>>>> Some requested scopes were invalid. {invalid=[l]}
> >>>>>>>
> >>>>>>> said that I hope you all agree this is an issue in the spec so
> far….
> >>>>>>>
> >>>>>>> regards
> >>>>>>>
> >>>>>>> antonio
> >>>>>>>
> >>>>>>>>
> >>>>>>>> John B.
> >>>>>>>>
> >>>>>>>> On Sep 3, 2014, at 12:10 PM, Bill Burke <[e-mail]
> >>>>>>>> <mailto:[e-mail]>
> >>>>>>>> <mailto:[e-mail]>> wrote:
> >>>>>>>>
> >>>>>>>>> I don't understand.  The redirect uri has to be valid in order
> for a
> >>>>>>>>> redirect to happen.  The spec explicitly states this.
> >>>>>>>>>
> >>>>>>>>>> On 9/3/2014 11:43 AM, Antonio Sanso wrote:
> >>>>>>>>>> hi *,
> >>>>>>>>>>
> >>>>>>>>>> IMHO providers that strictly follow rfc6749 are vulnerable to
> open
> >>>>>>>>>> redirect.
> >>>>>>>>>> Let me explain, reading [0]
> >>>>>>>>>>
> >>>>>>>>>> If the request fails due to a missing, invalid, or mismatching
> >>>>>>>>>> redirection URI, or if the client identifier is missing or
> invalid,
> >>>>>>>>>> the authorization server SHOULD inform the resource owner of the
> >>>>>>>>>> error and MUST NOT automatically redirect the user-agent to the
> >>>>>>>>>> invalid redirection URI.
> >>>>>>>>>>
> >>>>>>>>>> If the resource owner denies the access request or if the
> request
> >>>>>>>>>> fails for reasons other than a missing or invalid redirection
> URI,
> >>>>>>>>>> the authorization server informs the client by adding the
> following
> >>>>>>>>>> parameters to the query component of the redirection URI using
> the
> >>>>>>>>>> "application/x-www-form-urlencoded" format, perAppendix B
> >>>>>>>>>> <https://tools.ietf.org/html/rfc6749#appendix-B>:
> >>>>>>>>>>
> >>>>>>>>>> Now let’s assume this.
> >>>>>>>>>> I am registering a new client to thevictim.com
> >>>>>>>>>> <http://victim.com/><http://victim.com <http://victim.com/>>
> >>>>>>>>>> <http://victim.com <http://victim.com/>>
> >>>>>>>>>> provider.
> >>>>>>>>>> I register redirect uriattacker.com
> >>>>>>>>>> <http://attacker.com/><http://attacker.com <
> http://attacker.com/>>
> >>>>>>>>>> <http://attacker.com <http://attacker.com/>>.
> >>>>>>>>>>
> >>>>>>>>>> According to [0] if I pass e.g. the wrong scope I am redirected
> >>>>>>>>>> back to
> >>>>>>>>>> attacker.com <http://attacker.com/><http://attacker.com
> >>>>>>>>>> <http://attacker.com/>> <http://attacker.com <
> http://attacker.com/>>.
> >>>>>>>>>> Namely I prepare a url that is in this form:
> >>>>>>>>>>
> >>>>>>>>>>
> http://victim.com/authorize?response_type=code&client_id=bc88FitX1298KPj2WS259BBMa9_KCfL3&scope=WRONG_SCOPE&redirect_uri=http://attacker.com
> >>>>>>>>>>
> >>>>>>>>>> and this is works as an open redirector.
> >>>>>>>>>> Of course in the positive case if all the parameters are fine
> this
> >>>>>>>>>> doesn’t apply since the resource owner MUST approve the app via
> the
> >>>>>>>>>> consent screen (at least once).
> >>>>>>>>>>
> >>>>>>>>>> A solution would be to return error 400 rather than redirect to
> the
> >>>>>>>>>> redirect URI (as some provider e.g. Google do)
> >>>>>>>>>>
> >>>>>>>>>> WDYT?
> >>>>>>>>>>
> >>>>>>>>>> regards
> >>>>>>>>>>
> >>>>>>>>>> antonio
> >>>>>>>>>>
> >>>>>>>>>> [0] https://tools.ietf.org/html/rfc6749#section-4.1.2.1
> >>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>> _______________________________________________
> >>>>>>>>>> OAuth mailing list
> >>>>>>>>>> [e-mail]
> >>>>>>>>>> https://www.ietf.org/mailman/listinfo/oauth
> >>>>>>>>>
> >>>>>>>>> --
> >>>>>>>>> Bill Burke
> >>>>>>>>> JBoss, a division of Red Hat
> >>>>>>>>> http://bill.burkecentral.com
> >>>>>>>>>
> >>>>>>>>> _______________________________________________
> >>>>>>>>> OAuth mailing list
> >>>>>>>>> [e-mail] <mailto:[e-mail]>
> >>>>>>>>> https://www.ietf.org/mailman/listinfo/oauth
> >>>>>>>>
> >>>>>>>> _______________________________________________
> >>>>>>>> OAuth mailing list
> >>>>>>>> [e-mail] <mailto:[e-mail]><mailto:[e-mail]>
> >>>>>>>> https://www.ietf.org/mailman/listinfo/oauth
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> _______________________________________________
> >>>>>>> OAuth mailing list
> >>>>>>> [e-mail] <mailto:[e-mail]>
> >>>>>>> https://www.ietf.org/mailman/listinfo/oauth
> >>>>>>
> >>>>>> --
> >>>>>> Hans Zandbelt              | Sr. Technical Architect
> >>>>>> [e-mail] <mailto:[e-mail]>|
> Ping
> >>>>>> Identity
> >>>>
> >>>> --
> >>>> Hans Zandbelt              | Sr. Technical Architect
> >>>> [e-mail] | Ping Identity
> >>>
> >
> > --
> > Hans Zandbelt              | Sr. Technical Architect
> > [e-mail] | Ping Identity
> >
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