Re: [OAUTH-WG] OAuth 2.0 Security Best Current Practice | Issue in Mix-Up Countermeasure

Daniel Fett <fett@danielfett.de> Mon, 02 December 2019 10:26 UTC

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To: Christian Mainka <Christian.Mainka@rub.de>, oauth@ietf.org
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From: Daniel Fett <fett@danielfett.de>
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Date: Mon, 2 Dec 2019 11:26:19 +0100
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Subject: Re: [OAUTH-WG] OAuth 2.0 Security Best Current Practice | Issue in Mix-Up Countermeasure
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Am 02.12.19 um 10:05 schrieb Christian Mainka:
> I think this problem is not only restricted to the redirect_uri.
> Regarding countermeasure (1), also the A-AS can return the same
> client_id as the client uses on the H-AS.
>
> TL;DR: In countermeasure (1), only the issuer prevents MixUp, the
> client_id parameter can be faked as well during the registration of the
> client (especially if Dynamic Client Registration is used).

What would be the issuer identifiers of A-AS and H-AS in this case be,
as seen by the client?

-Daniel