The biggest problem with this attack is the passing of the access token to a 
backend server (and its subsequent passing of that token to someone else) and 
the assumption that the presentation of the access token means that the user is 
authenticated and present. It simply doesn't mean that, and this is a bad 
assumption that unfortunately many people make thanks to providers like 
Facebook using OAuth (or, mostly-OAuth since they're not actually RFC 
compliant) in the authentication protocol.

It's also a problem that so many people are using the implicit flow "because 
it's easy", missing the point of why it's there in the first place. The 
implicit flow is really only intended for cases where you can't hide secrets 
from the user agent, cases like an in-browser application. The flow diagrams 
that you have don't fit the implicit flow very well at all, since the access 
token is getting passed back to some other service. 

 -- Justin

On May 13, 2013, at 11:14 AM, Antonio Sanso <asa...@adobe.com>
 wrote:

> Hi *,
> 
> I wrote a blog post showing two well known OAuth related attacks. I paste 
> here the link for your consideration:
> 
> http://intothesymmetry.blogspot.ch/2013/05/oauth-2-attacks-introducing-devil-wears.html
> 
> Any comment is more than appreciated.
> 
> Regards
> 
> Antonio
> _______________________________________________
> OAuth mailing list
> OAuth@ietf.org
> https://www.ietf.org/mailman/listinfo/oauth

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