Re: [OAUTH-WG] Call for Adoption: OAuth 2.0 Mix-Up Mitigation

[Justin Richer <[e-mail]>]

I propose we rename this the “Random ASs Attack”.

 — Justin (only half joking)

> On Jan 27, 2016, at 8:07 AM, Nat Sakimura <[e-mail]> wrote:
> 
> Yup. 
> 
> For the RPs that would deal with valuable data, I also recommend it to become HTTPS only. This will effectively close the hole for the AS Mix-Up. 
> Also, I would recommend to the clients to think twice before accepting random ASs. 
> To prevent the code phishing, it is a good idea to require the same authority restriction. Otherwise, use some variant of discovery to get the authoritative token endpoints. 
> 
> 
> 2016年1月27日(水) 21:49 George Fletcher <[e-mail] <mailto:[e-mail]>>:
> Based on Hans' response to Nat I understand why this doesn't solve all the use cases. It does still seem like a good idea from a client perspective that would address the dynamic client registration cases where the Bad AS is returning mixed endpoints.
> 
> 
> On 1/27/16 7:43 AM, George Fletcher wrote:
>> Following up on Nat's last paragraph... did the group in Darmstadt discuss this option? Namely, to require that the authority section of the AuthZ and Token endpoints be the same? Are there known implementations already deployed where the authority sections are different? It seems like a simple check that would address the endpoint mix-up cases.
>> 
>> Thanks,
>> George
>> 
>> On 1/26/16 8:58 PM, Nat Sakimura wrote:
>>> John, 
>>> 
>>> Nov is not talking about the redirection endpoint. I just noticed that 3.1.2.1 of RFC 6749 is just asking TLS by "SHOULD" and I think it needs to be changed to "MUST" but that is not what he is talking about. 
>>> 
>>> Instead, he is talking about before starting the RFC 6749 flow. 
>>> 
>>> In many cases, a non TLS protected sites have "Login with HIdP" button linked to a URI that initiates the RFC 6749 flow. This portion is not within  RFC 6749 and this endpoint has no name or no requirement to be TLS protected. Right, it is very stupid, but there are many sites like that. 
>>> As a result, the attacker can insert itself as a proxy, say by providing a free wifi hotspot, and either re-write the button or the request so that the RP receives "Login with AIdP" instead of "Login with HIdP". 
>>> 
>>> I have add a note explaining this to  <http://nat.sakimura.org/2016/01/15/idp-mix-up-attack-on-oauth-rfc6749/>http://nat.sakimura.org/2016/01/15/idp-mix-up-attack-on-oauth-rfc6749/ <http://nat.sakimura.org/2016/01/15/idp-mix-up-attack-on-oauth-rfc6749/>
>>> 
>>> I also have added a bit of risk analysis on it and considered other risk control measures as well. 
>>> 
>>> It does not seem to be worthwhile to introduce a new wire-protocol element to deal with this particular attack. (I regard code cut-and-paste attack a separate attack.) I am inclining to think that just to TLS protect the pre-RFC6749 flow portion and add a check to disallow the ASs that has different authority section for the Auhtz EP and Token EP would be adequate. 
>>> 
>>> Nat
>>> 
>>> 2016年1月27日(水) 2:18 John Bradley < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>>:
>>> Nov,
>>> 
>>> Are you referring to Sec 3.1.2.1 of RFC 6749.
>>> 
>>> Stating that the the redirection endpoint SHOULD require TLS, and that the AS should warn the user if the redirect URI is not over TLS (Something I have never seen done in the real world)
>>> 
>>> Not using TLS is reasonable when the redirect URI is using a custom scheme for native apps.
>>> 
>>> It might almost be reasonable for the token flow where the JS page itself is not loaded over TLS so the callback to extract the fragment would not be as well. 
>>> Note that the token itself is never passed over a non https connection in tis case.
>>> I would argue now that it is irresponsible to have a non TLS protected site, but not everyone is going to go along with that.  
>>> 
>>> Using a http scheme URI for the redirect is allowed but is really stupid.   We did have a large debate about this when profiling OAuth for Connect.
>>> We did tighten connect to say that if you are using the code flow then a http scheme redirect URI is only allowed if the client is confidential. 
>>> 
>>> John B.
>>>> On Jan 26, 2016, at 1:14 AM, Phil Hunt (IDM) <[e-mail] <mailto:[e-mail]>> wrote:
>>>> 
>>>> Still don't see it. Though i think the diagram is wrong (the rp should redirct to the ua and not call the authz direct), the IDP should either return an error or redirect the RP to TLS. 
>>>> 
>>>> I don't see this as proper oauth protocol since the RP is MITM the UA rather than acting as a client. 
>>>> 
>>>> Phil
>>>> 
>>>> On Jan 25, 2016, at 19:57, nov matake < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>> wrote:
>>>> 
>>>>> In this flow, AuthZ endpoint is forced to be TLS-protected.
>>>>> http://nat.sakimura.org/wp-content/uploads/2016/01/oauth-idp-mixup.png <http://nat.sakimura.org/wp-content/uploads/2016/01/oauth-idp-mixup.png>
>>>>> 
>>>>> However, RP’s redirect response which causes following AuthZ request is still not TLS-protected, and modified on the attacker’s proxy.
>>>>> 
>>>>> Section 3.2 of this report also describes the same flow.
>>>>> http://arxiv.org/pdf/1601.01229v2.pdf <http://arxiv.org/pdf/1601.01229v2.pdf>
>>>>> 
>>>>>> On Jan 26, 2016, at 12:37, Phil Hunt (IDM) < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>> wrote:
>>>>>> 
>>>>>> Also the authz endpoint is required to force tls. So if the client doesn't do it the authz should reject (eg by upgrading to tls). 
>>>>>> 
>>>>>> Phil
>>>>>> 
>>>>>> On Jan 25, 2016, at 19:29, Phil Hunt (IDM) < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>> wrote:
>>>>>> 
>>>>>>> When the RP acting as the client issues a authorize redirect to the UA it has to make it with TLS
>>>>>>> 
>>>>>>> Phil
>>>>>>> 
>>>>>>> On Jan 25, 2016, at 17:53, Nov Matake < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>> wrote:
>>>>>>> 
>>>>>>>> It doen't say anything about the first request which initiate the login flow.
>>>>>>>> It is still a reasonable assumption that RP puts a "login with FB" button on a non TLS-protected page.
>>>>>>>> 
>>>>>>>> nov
>>>>>>>> 
>>>>>>>> On Jan 26, 2016, at 10:45, Phil Hunt < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>> wrote:
>>>>>>>> 
>>>>>>>>> I would find it hard to believe that is true.
>>>>>>>>> 
>>>>>>>>> From 6749 Sec 3.1 
>>>>>>>>>    Since requests to the authorization endpoint result in user
>>>>>>>>>    authentication and the transmission of clear-text credentials (in the
>>>>>>>>>    HTTP response), the authorization server MUST require the use of TLS
>>>>>>>>>    as described in Section 1.6 <https://tools.ietf.org/html/rfc6749#section-1.6> when sending requests to the
>>>>>>>>>    authorization endpoint.
>>>>>>>>> 
>>>>>>>>> Sec 3.1.2.1 
>>>>>>>>>    The redirection endpoint SHOULD require the use of TLS as described
>>>>>>>>>    in Section 1.6 <https://tools.ietf.org/html/rfc6749#section-1.6> when the requested response type is "code" or "token",
>>>>>>>>>    or when the redirection request will result in the transmission of
>>>>>>>>>    sensitive credentials over an open network.  This specification does
>>>>>>>>>    not mandate the use of TLS because at the time of this writing,
>>>>>>>>>    requiring clients to deploy TLS is a significant hurdle for many
>>>>>>>>>    client developers.  If TLS is not available, the authorization server
>>>>>>>>>    SHOULD warn the resource owner about the insecure endpoint prior to
>>>>>>>>>    redirection (e.g., display a message during the authorization
>>>>>>>>>    request).
>>>>>>>>> 
>>>>>>>>>    Lack of transport-layer security can have a severe impact on the
>>>>>>>>>    security of the client and the protected resources it is authorized
>>>>>>>>>    to access.  The use of transport-layer security is particularly
>>>>>>>>>    critical when the authorization process is used as a form of
>>>>>>>>>    delegated end-user authentication by the client (e.g., third-party
>>>>>>>>>    sign-in service).
>>>>>>>>> 
>>>>>>>>> Section 10.5 talks about transmission of authorization codes in connection with redirects.
>>>>>>>>> 
>>>>>>>>> Also see 6819, Sec 4.4.1.1 regarding eavesdropping or leaking of authz codes.
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> Phil
>>>>>>>>> 
>>>>>>>>> @independentid
>>>>>>>>>  <http://www.independentid.com/>www.independentid.com <http://www.independentid.com/> <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>>> On Jan 25, 2016, at 4:52 PM, nov matake < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>> wrote:
>>>>>>>>>> 
>>>>>>>>>> The first assumption is coming from the original security report at  <http://arxiv.org/abs/1601.01229>http://arxiv.org/abs/1601.01229 <http://arxiv.org/abs/1601.01229>.
>>>>>>>>>> RFC 6749 requires TLS between RS and AS, and also between UA and AS, but not between UA and RS.
>>>>>>>>>> 
>>>>>>>>>> The blog post is based on my Japanese post, and it describes multi-AS case.
>>>>>>>>>> Nat's another post describes the case which can affect single-AS case too.
>>>>>>>>>>  <http://nat.sakimura.org/2016/01/22/code-phishing-attack-on-oauth-2-0-rfc6749/>http://nat.sakimura.org/2016/01/22/code-phishing-attack-on-oauth-2-0-rfc6749/ <http://nat.sakimura.org/2016/01/22/code-phishing-attack-on-oauth-2-0-rfc6749/>
>>>>>>>>>> 
>>>>>>>>>> nov
>>>>>>>>>> 
>>>>>>>>>>> On Jan 26, 2016, at 08:22, Phil Hunt < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>> wrote:
>>>>>>>>>>> 
>>>>>>>>>>> Sorry, meant to reply-all.
>>>>>>>>>>> 
>>>>>>>>>>> Phil
>>>>>>>>>>> 
>>>>>>>>>>> @independentid
>>>>>>>>>>>  <http://www.independentid.com/>www.independentid.com <http://www.independentid.com/> <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>>> Begin forwarded message:
>>>>>>>>>>>> 
>>>>>>>>>>>> From: Phil Hunt <[e-mail] <mailto:[e-mail]>>
>>>>>>>>>>>> Subject: Re: [OAUTH-WG] Call for Adoption: OAuth 2.0 Mix-Up Mitigation
>>>>>>>>>>>> Date: January 25, 2016 at 3:20:19 PM PST
>>>>>>>>>>>> To: Nat Sakimura <[e-mail] <mailto:[e-mail]>>
>>>>>>>>>>>> 
>>>>>>>>>>>> I am having trouble with the very first assumption. The user-agent sets up a non TLS protected connection to the RP? That’s a fundamental violation of 6749.
>>>>>>>>>>>> 
>>>>>>>>>>>> Also, the second statement says the RP (assuming it acts as OAuth client) is talking to two IDPs.  That’s still a multi-AS case is it not?
>>>>>>>>>>>> 
>>>>>>>>>>>> Phil
>>>>>>>>>>>> 
>>>>>>>>>>>> @independentid
>>>>>>>>>>>>  <http://www.independentid.com/>www.independentid.com <http://www.independentid.com/> <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>
>>>>>>>>>>>> 
>>>>>>>>>>>> 
>>>>>>>>>>>> 
>>>>>>>>>>>> 
>>>>>>>>>>>> 
>>>>>>>>>>>>> On Jan 25, 2016, at 2:58 PM, Nat Sakimura < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>> wrote:
>>>>>>>>>>>>> 
>>>>>>>>>>>>> Hi Phil, 
>>>>>>>>>>>>> 
>>>>>>>>>>>>> Since I was not in Darmstadt, I really do not know what was discussed there, but with the compromised developer documentation described in  <http://nat.sakimura.org/2016/01/15/idp-mix-up-attack-on-oauth-rfc6749/>http://nat.sakimura.org/2016/01/15/idp-mix-up-attack-on-oauth-rfc6749/ <http://nat.sakimura.org/2016/01/15/idp-mix-up-attack-on-oauth-rfc6749/>, all RFC6749 clients with a naive implementer will be affected. The client does not need to be talking to multiple IdPs. 
>>>>>>>>>>>>> 
>>>>>>>>>>>>> Nat
>>>>>>>>>>>>> 
>>>>>>>>>>>>> 2016 年1月26日(火) 3:58 Phil Hunt (IDM) < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>>:
>>>>>>>>>>>>> I recall making this point in Germany. 99% of existing use is fine. OIDC is probably the largest community that *might* have an issue.
>>>>>>>>>>>>> 
>>>>>>>>>>>>> I recall proposing a new security document that covers oauth security for dynamic scenarios. "Dynamic" being broadly defined to mean:
>>>>>>>>>>>>> * clients who have configured at runtime or install time (including clients that do discovery)
>>>>>>>>>>>>> * clients that communicate with more than one endpoint
>>>>>>>>>>>>> * clients that are deployed in large volume and may update frequently (more discussion of "public" cases)
>>>>>>>>>>>>> * clients that are script based (loaded into browser on the fly)
>>>>>>>>>>>>> * others?
>>>>>>>>>>>>> 
>>>>>>>>>>>>> Phil
>>>>>>>>>>>>> 
>>>>>>>>>>>>> > On Jan 25, 2016, at 10:39, George Fletcher < <mailto:[e-mail]>[e-mail] <mailto:[e-mail]>> wrote:
>>>>>>>>>>>>> >
>>>>>>>>>>>>> > would
>>>>>>>>>>>>> 
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>>>>>>>>>>>> 
>>>>>>>>>>> 
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