Re: [OAUTH-WG] Multi-AS State Re-Use

As far as I am aware of, state was meant to be nonce. Replay possibility
etc. were known. It is probably a bad documentation that every reviewers
missed because they were assuming it.

Best,

Nat
On Mon, May 9, 2016 at 20:14 Guido Schmitz <g.schmitz@gtrs.de> wrote:

> Hi all,
>
> can anybody confirm that this is a new / undocumented attack?
>
> Cheers,
>
> Guido, Daniel, and Ralf
>
> On 22.04.2016 16:23, Daniel Fett wrote:
> > Hi all,
> >
> > Besides the state leakage attack we found that another important fact
> > regarding state is underspecified: Each state value should only be
> > used for one run of the protocol, in particular, each AS should see a
> > different state in multi-AS settings. Clients might be tempted to
> > generate state once and then re-use each time a user wants to
> > authorize.
> >
> > If state is re-used, given a setup where one Client allows users to
> > authorize using two AS, a potentially malicious AS learns the state
> > value that is valid for authorization at an honest AS. I.e., each AS
> > can mount a CSRF attack on the user using the other AS.
> >
> > Just as the attack in the other mail, this is not a big deal in
> > practice, but should be discussed somewhere.
> >
> > Cheers,
> > Daniel, Guido, and Ralf
> >
>
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-- 
Nat Sakimura
Chairman of the Board, OpenID Foundation
Trustee, Kantara Initiative