Re: [OAUTH-WG] Report an authentication issue

[John Bradley <[e-mail]>]

The attack requires a web browser that allows modifying the value of the of the redirect URI.   It is dead simple cut token or code from the string and paste in the token or code that was granted by the user you want to impersonate.

OAuth responses are not signed or audience restricted to the client(except confidential clients using the code flow).  

In cases where the code or token is passed over a back channel to a server, faking the entire client is the easiest thing for the attacker.

I don't consider these to be authorization attacks,  rather attacks on a client that is inappropariatly making unwarranted assumptions about the presenter of the token.

John B.
On 2012-06-29, at 3:29 PM, Phil Hunt wrote:

> We need more info on the inject method the researchers used before we can account for it. 
> 
> Phil
> 
> On 2012-06-29, at 12:16, John Bradley <[e-mail]> wrote:
> 
>> The same thing can be done with code.
>> 
>> If the token endpoint checks the client_id before giving out the access token then the attack on code can be prevented, as the token endpoint won't return the access token.
>> 
>> The spec dosen't require authenticating public clients currently so it is a slightly more difficult attack but possible.
>> 
>> Dick and I are suggesting closing the hole at the token endpoint so that nether confidential nor public clients using the code flow are susceptible to this substitution attack.
>> 
>> John B.
>> 
>> On 2012-06-29, at 2:53 PM, PhiIt helps with the code flow when l Hunt wrote:
>> 
>>> I'm not seeing how client id helps if a proxy server is somehow involved with inserting the bearer token as the researchers suggested. 
>>> 
>>> Phil
>>> 
>>> On 2012-06-29, at 11:30, John Bradley <[e-mail]> wrote:
>>> 
>>>> I think they only exploited the implicit flow.   
>>>> 
>>>> My point was that there is a way you could do the same thing with code if it is a public client that is not authenticating to the token endpoint.
>>>> 
>>>> In general making identity assumptions in the client based on a code or access_token has risks that are out of scope for OAuth.
>>>> 
>>>> We do however want to provide good advice about specific things that can leave systems insecure when using OAuth.
>>>> 
>>>> John B.
>>>> 
>>>> On 2012-06-29, at 2:22 PM, Phil Hunt wrote:
>>>> 
>>>>> I'm not clear whether the MS Security Researcher hack was with the authorization code or the access token. If the latter, the client_id is out of the picture isn't it?
>>>>> 
>>>>> Phil
>>>>> 
>>>>> @independentid
>>>>> www.independentid.com
>>>>> [e-mail]
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> On 2012-06-29, at 11:14 AM, Dick Hardt wrote:
>>>>> 
>>>>>> 
>>>>>> On Jun 29, 2012, at 11:06 AM, John Bradley wrote:
>>>>>> 
>>>>>>> It is nice to know that I may occasionally be correct:)
>>>>>> 
>>>>>> You must be delighted when it happens! ;)
>>>>>> 
>>>>>>> While you may assume that it is reasonable for a client with a code to make a request to the token endpoint including it's client_id and the server to only give out the access token if the client_id in the token request matches the one in the original authorization request.   However the spec specifically doesn't require that.
>>>>>> 
>>>>>> I think that is an error in the spec and should be changed, or text adding saying that the client_id SHOULD be checked.
>>>>>> 
>>>>>> -- Dick
>>>>>> _______________________________________________
>>>>>> OAuth mailing list
>>>>>> [e-mail]
>>>>>> https://www.ietf.org/mailman/listinfo/oauth
>>>>> 
>>>> 
>>