On Sep 4, 2014, at 2:22 PM, John Bradley <ve7...@ve7jtb.com> wrote: > Registration requiring a valid email address is not sufficient to stop a > "bad" person from registering a client that appears to be perfectly > legitimate but is later used as a redirect.
totally agree! > > So it is a bit slippery to differentiate good from bad. > > In general clearing the referrer and fragment from incoming requests is a > good practice on redirects to prevent leakage of information across the > redirect. +1 > > The other concern is using the redirect as part of a phishing attack to make > the target site look more legitimate. > That is a more complicated problem unless you validate every client by > looking at them to make sure they are not bad in some way. and here it comes the "error 400" or the "always show the consent screen” approach regards antonio > > John B. > > > On Sep 4, 2014, at 2:09 PM, Hans Zandbelt <hzandb...@pingidentity.com> wrote: > >> Maybe just to clarify my point: where did the client_id in the example that >> you gave come from? >> >> Hans. >> >> On 9/4/14, 1:58 PM, Hans Zandbelt wrote: >>> yes, you are right about the unrestricted client use case; I just got >>> caught by the fact that you were talking about *unrestricted* client >>> registration all the time (standards-based or not) which deserves extra >>> caution whereas Google (and the spec) also provides *restricted* client >>> registration the deviation or caution is not needed >>> >>> Hans. >>> >>> On 9/4/14, 1:44 PM, Antonio Sanso wrote: >>>> hi Hans >>>> >>>> On Sep 4, 2014, at 10:58 AM, Hans Zandbelt >>>> <hzandb...@pingidentity.com> wrote: >>>> >>>>> Agreed, I see you point about the big providers using exactly the >>>>> unrestricted flow for which the trust model (by definition) is out of >>>>> scope of the spec. This may be the reason for the implemented >>>>> behavior indeed and a security consideration is a good idea for other >>>>> deployments; there's not much more that can be done. >>>>> >>>>> But Google also provides explicit registration for API clients (which >>>>> is where my mind was): >>>>> https://developers.google.com/accounts/docs/OAuth2 (step 1) >>>>> and they would not need to deviate from the spec for that, nor would >>>>> the spec need to change >>>> >>>> I do really struggle to understand your point here :) (at least the >>>> "nor would the spec need to change part" :)). >>>> >>>> Probably I need to explain myself better. >>>> Since Google is “safe” (due the “deviation” from the spec) I would >>>> take Google as example here (I could point out open redirector in the >>>> wild to proof my point but I will not do…) >>>> >>>> Let’s start from scratch… >>>> >>>> If Google would have something like >>>> http://www.google.com?goto=attacker.com this is without any doubt an >>>> open redirector… see also OWASP 10 [0]. >>>> >>>> Now if Google would have implemented the spec rfc6749 verbatim >>>> something like >>>> >>>> https://accounts.google.com/o/oauth2/auth?response_type=code&client_id=788732372078.apps.googleusercontent.com&scope=WRONG_SCOPE&redirect_uri=http://attacker.com >>>> >>>> >>>> would have redirect to http://attacker.com. >>>> >>>> So why this is not an open redirect ? :) >>>> >>>> Now maybe we are saying the same thing but I felt like better explain >>>> my point :) >>>> >>>> regards >>>> >>>> antonio >>>> >>>> [0] >>>> https://www.owasp.org/index.php/Top_10_2010-A10-Unvalidated_Redirects_and_Forwards >>>> >>>> >>>> >>>>> >>>>> Hans. >>>>> >>>>> On 9/4/14, 9:50 AM, Antonio Sanso wrote: >>>>>> Hi Hans, >>>>>> >>>>>> I really fail to see how this can be addressed at registration time >>>>>> for cases where registration is unrestricted (namely all the big >>>>>> Providers) >>>>>> >>>>>> regards >>>>>> >>>>>> antonio >>>>>> >>>>>> On Sep 4, 2014, at 9:47 AM, Hans Zandbelt >>>>>> <hzandb...@pingidentity.com> wrote: >>>>>> >>>>>>> Classifying like this must also mean that consent should not be >>>>>>> stored until the client is considered (admin) trusted, and admin >>>>>>> policy would interfere with user policy. >>>>>>> >>>>>>> IMHO the security consideration would apply only to dynamically >>>>>>> registered clients where registration is unrestricted; any other >>>>>>> form would involve some form of admin/user approval at registration >>>>>>> time, overcoming the concern at authorization time: there's no >>>>>>> auto-redirect flow possible for unknown clients. >>>>>>> >>>>>>> Hans. >>>>>>> >>>>>>> On 9/4/14, 9:04 AM, Richer, Justin P. wrote: >>>>>>>> I think this advice isn't a bad idea, though it's of course up to >>>>>>>> the AS >>>>>>>> what an "untrusted" client really is. In practice, this is something >>>>>>>> that was registered by a non-sysadmin type person, either a >>>>>>>> dynamically >>>>>>>> registered client or something available through self-service >>>>>>>> registration of some type. It's also reasonable that a client, even >>>>>>>> dynamically registered, would be considered "trusted" if enough >>>>>>>> time has >>>>>>>> passed and enough users have used it without things blowing up. >>>>>>>> >>>>>>>> -- Justin >>>>>>>> >>>>>>>> On Sep 4, 2014, at 1:26 AM, Antonio Sanso <asa...@adobe.com >>>>>>>> <mailto:asa...@adobe.com>> wrote: >>>>>>>> >>>>>>>>> hi again *, >>>>>>>>> >>>>>>>>> after thinking a bit further IMHO an alternative for the untrusted >>>>>>>>> clients can also be to always present the consent screen (at least >>>>>>>>> once) before any redirect. >>>>>>>>> Namely all providers I have seen show the consent screen if all the >>>>>>>>> request parameters are correct and if the user accepts the redirect >>>>>>>>> happens. >>>>>>>>> If one of the parameter (with the exclusion of the client id and >>>>>>>>> redirect uri that are handled differently as for spec) is wrong >>>>>>>>> though >>>>>>>>> the redirect happens without the consent screen being shown.. >>>>>>>>> >>>>>>>>> WDYT? >>>>>>>>> >>>>>>>>> regards >>>>>>>>> >>>>>>>>> antonio >>>>>>>>> >>>>>>>>> On Sep 3, 2014, at 7:54 PM, Antonio Sanso <asa...@adobe.com >>>>>>>>> <mailto:asa...@adobe.com>> wrote: >>>>>>>>> >>>>>>>>>> Well, >>>>>>>>>> I do not know if this is only dynamic registration... >>>>>>>>>> let’s talk about real use cases, namely e.g. Google , Facebook , >>>>>>>>>> etc.. is that dynamic client registration? I do not know… :) >>>>>>>>>> >>>>>>>>>> Said that what the other guys think? :) >>>>>>>>>> Would this deserve some “spec adjustment” ? I mean there is a >>>>>>>>>> reason >>>>>>>>>> if Google is by choice “violating” the spec right? (I assume to >>>>>>>>>> avoid >>>>>>>>>> open redirect…) >>>>>>>>>> But other implementers do follow the spec hence they have this open >>>>>>>>>> redirector… and this is not nice IMHO... >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> On Sep 3, 2014, at 7:40 PM, Hans Zandbelt >>>>>>>>>> <hzandb...@pingidentity.com >>>>>>>>>> <mailto:hzandb...@pingidentity.com>> wrote: >>>>>>>>>> >>>>>>>>>>> On 9/3/14, 7:14 PM, Antonio Sanso wrote: >>>>>>>>>>>> >>>>>>>>>>>> On Sep 3, 2014, at 7:10 PM, Hans Zandbelt >>>>>>>>>>>> <hzandb...@pingidentity.com >>>>>>>>>>>> <mailto:hzandb...@pingidentity.com>> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> Is your concern clients that were registered using dynamic >>>>>>>>>>>>> client >>>>>>>>>>>>> registration? >>>>>>>>>>>> >>>>>>>>>>>> yes >>>>>>>>>>> >>>>>>>>>>> I think your issue is then with the trust model of dynamic client >>>>>>>>>>> registration; that is left out of scope of the dynreg spec (and >>>>>>>>>>> the >>>>>>>>>>> concept is not even part of the core spec), but unless you want >>>>>>>>>>> everything to be open (which typically would not be the case), >>>>>>>>>>> then >>>>>>>>>>> it would involve approval somewhere in the process before the >>>>>>>>>>> client >>>>>>>>>>> is registered. Without dynamic client registration that >>>>>>>>>>> approval is >>>>>>>>>>> admin based or resource owner based, depending on use case. >>>>>>>>>>> >>>>>>>>>>>>> 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… >>>>>>>>>>> >>>>>>>>>>> roles can collapse in use cases especially when using dynamic >>>>>>>>>>> client >>>>>>>>>>> registration >>>>>>>>>>> >>>>>>>>>>>>> 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? >>>>>>>>>>> >>>>>>>>>>> because the client and thus the fixed URL are explicitly >>>>>>>>>>> approved at >>>>>>>>>>> some point >>>>>>>>>>> >>>>>>>>>>> Hans. >>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> Hans. >>>>>>>>>>>>> >>>>>>>>>>>>> On 9/3/14, 6:56 PM, Antonio Sanso wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>> On Sep 3, 2014, at 6:51 PM, Hans Zandbelt >>>>>>>>>>>>>> <hzandb...@pingidentity.com <mailto:hzandb...@pingidentity.com> >>>>>>>>>>>>>> <mailto:hzandb...@pingidentity.com>> 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 <ve7...@ve7jtb.com >>>>>>>>>>>>>>>> <mailto:ve7...@ve7jtb.com> >>>>>>>>>>>>>>>> <mailto:ve7...@ve7jtb.com> >>>>>>>>>>>>>>>> <mailto:ve7...@ve7jtb.com>> 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 <bbu...@redhat.com >>>>>>>>>>>>>>>>> <mailto:bbu...@redhat.com> >>>>>>>>>>>>>>>>> <mailto:bbu...@redhat.com> >>>>>>>>>>>>>>>>> <mailto:bbu...@redhat.com>> 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://thevictim.com/> >>>>>>>>>>>>>>>>>>> <http://victim.com/><http://victim.com >>>>>>>>>>>>>>>>>>> <http://victim.com/> >>>>>>>>>>>>>>>>>>> <http://victim.com/>> >>>>>>>>>>>>>>>>>>> <http://victim.com <http://victim.com/> >>>>>>>>>>>>>>>>>>> <http://victim.com/>> >>>>>>>>>>>>>>>>>>> provider. >>>>>>>>>>>>>>>>>>> I register redirect uriattacker.com >>>>>>>>>>>>>>>>>>> <http://uriattacker.com/> >>>>>>>>>>>>>>>>>>> <http://attacker.com/><http://attacker.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/>> <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 >>>>>>>>>>>>>>>>>>> OAuth@ietf.org <mailto:OAuth@ietf.org> >>>>>>>>>>>>>>>>>>> https://www.ietf.org/mailman/listinfo/oauth >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> -- >>>>>>>>>>>>>>>>>> Bill Burke >>>>>>>>>>>>>>>>>> JBoss, a division of Red Hat >>>>>>>>>>>>>>>>>> http://bill.burkecentral.com >>>>>>>>>>>>>>>>>> <http://bill.burkecentral.com/> >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> _______________________________________________ >>>>>>>>>>>>>>>>>> OAuth mailing list >>>>>>>>>>>>>>>>>> OAuth@ietf.org <mailto:OAuth@ietf.org> >>>>>>>>>>>>>>>>>> <mailto:OAuth@ietf.org> >>>>>>>>>>>>>>>>>> https://www.ietf.org/mailman/listinfo/oauth >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> _______________________________________________ >>>>>>>>>>>>>>>>> OAuth mailing list >>>>>>>>>>>>>>>>> OAuth@ietf.org <mailto:OAuth@ietf.org> >>>>>>>>>>>>>>>>> <mailto:OAuth@ietf.org><mailto:OAuth@ietf.org> >>>>>>>>>>>>>>>>> https://www.ietf.org/mailman/listinfo/oauth >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> _______________________________________________ >>>>>>>>>>>>>>>> OAuth mailing list >>>>>>>>>>>>>>>> OAuth@ietf.org <mailto:OAuth@ietf.org> >>>>>>>>>>>>>>>> <mailto:OAuth@ietf.org> >>>>>>>>>>>>>>>> https://www.ietf.org/mailman/listinfo/oauth >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> -- >>>>>>>>>>>>>>> Hans Zandbelt | Sr. Technical Architect >>>>>>>>>>>>>>> hzandb...@pingidentity.com <mailto:hzandb...@pingidentity.com> >>>>>>>>>>>>>>> <mailto:hzandb...@pingidentity.com>| Ping >>>>>>>>>>>>>>> Identity >>>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>> -- >>>>>>>>>>>>> Hans Zandbelt | Sr. Technical Architect >>>>>>>>>>>>> hzandb...@pingidentity.com <mailto:hzandb...@pingidentity.com> | >>>>>>>>>>>>> Ping Identity >>>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> -- >>>>>>>>>>> Hans Zandbelt | Sr. Technical Architect >>>>>>>>>>> hzandb...@pingidentity.com <mailto:hzandb...@pingidentity.com>| >>>>>>>>>>> Ping >>>>>>>>>>> Identity >>>>>>>>>> >>>>>>>>> >>>>>>>>> _______________________________________________ >>>>>>>>> OAuth mailing list >>>>>>>>> OAuth@ietf.org <mailto:OAuth@ietf.org> >>>>>>>>> https://www.ietf.org/mailman/listinfo/oauth >>>>>>>> >>>>>>> >>>>>>> -- >>>>>>> Hans Zandbelt | Sr. Technical Architect >>>>>>> hzandb...@pingidentity.com | Ping Identity >>>>>> >>>>> >>>>> -- >>>>> Hans Zandbelt | Sr. Technical Architect >>>>> hzandb...@pingidentity.com | Ping Identity >>>> >>> >> >> -- >> Hans Zandbelt | Sr. Technical Architect >> hzandb...@pingidentity.com | Ping Identity >> >> _______________________________________________ >> OAuth mailing list >> OAuth@ietf.org >> https://www.ietf.org/mailman/listinfo/oauth > _______________________________________________ OAuth mailing list OAuth@ietf.org https://www.ietf.org/mailman/listinfo/oauth
