Re: [OAUTH-WG] Mix-Up About The Mix-Up Mitigation

Bill Mills <> Wed, 13 January 2016 19:36 UTC

Return-Path: <>
Received: from localhost ( []) by (Postfix) with ESMTP id 8CF151B313E for <>; Wed, 13 Jan 2016 11:36:52 -0800 (PST)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.6
X-Spam-Status: No, score=-1.6 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001, FREEMAIL_REPLYTO_END_DIGIT=0.25, HTML_MESSAGE=0.001, J_CHICKENPOX_25=0.6, RCVD_IN_DNSWL_LOW=-0.7, RP_MATCHES_RCVD=-0.001, SPF_PASS=-0.001] autolearn=no
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id 3IJMgWL_bBoA for <>; Wed, 13 Jan 2016 11:36:50 -0800 (PST)
Received: from ( []) (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 425951B313C for <>; Wed, 13 Jan 2016 11:36:50 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=s2048; t=1452713809; bh=G+0tP5J+xRlhEZ8SSgFfGiU8bfGkjMnv+bJu0jHBl+M=; h=Date:From:Reply-To:To:Cc:In-Reply-To:References:Subject:From:Subject; b=kPGW6LyK2jdvFwCurWE0gSLIp/C3uRuZsLcsN/y8GK2UdV/ozU/PHd8yNnCJr6cMRE0fY4uol02Aus/i6/mxbHYzA9sFzb7dd72239imN/Jo+RFAyvDhLx2dr0whbWI69gs9436EHm2g0gVswS3bZMHLjRzTTLZfdplu8FCS6dduUVbtRkhK6rxCt7unxslvaWEaUzbq6TCXmC/YytRwDLeN2Dy1t4TO5ZgBmOkzeNuxA1Xqet1vLwz2UWpNG/MbmRScBq5aje7GShCKEi0ElgpKEm1GK/2+jkckfd+jlNzI3uohaim0fAsZhfReI0A6b0mpSb7qYJsIA/PpDoHZXg==
Received: from [] by with NNFMP; 13 Jan 2016 19:36:49 -0000
Received: from [] by with NNFMP; 13 Jan 2016 19:36:49 -0000
Received: from [] by with NNFMP; 13 Jan 2016 19:36:49 -0000
X-Yahoo-Newman-Property: ymail-3
X-YMail-OSG: TqIpJSMVM1nMaEaKf_e1EV.WB8DhfoaVQTKhHDJOQhQVuchhpubF.XWygSAaKgU ehwb4bvxF.RLoPtSqpIeEdO__obzXQiJCaHDigdeUHCZx3LM023417BppfmbVdq96MQYw0vbbW5T O4q7i6t5zTitJsBmlVDoQjBZT2KNLSk7o1PVPuI5uRbnn88_kbqRO7bLeNc0ulSw2yuc1Prxzl_6 xaDVl4bbmmXmUDFeNuJxYc_bMppdsGAMLDXBxzRMx0_gRIqi1_MWg1YWv5lepxwm7oiiBC.JUw3P PRq1Roz2zol_9ZyWJ3IjYLY2bQ82Em422txP7zL3LqKTY0TUbHuf98vZUt3AsoXyRpiDTStyKFUF EbA0jyYkkwUOVgCTfLYRZsCugJ_u6gXegtb3B0WxzOXcoQ0pV.YimU2.Y4guBpYw3pUdL1d8wX8m 8WgMfAWzpSwzxkvAk2JU6Bk9mX5n1pE3LnH8ftAMG03GUhI21PBq6Ul7xjxYROWkZoZOE_WXN07B d6hIc7C5c2NFK_i3.LblLQI4cOl4CZPPHFteN
Received: by; Wed, 13 Jan 2016 19:36:48 +0000
Date: Wed, 13 Jan 2016 19:36:48 +0000
From: Bill Mills <>
To: Justin Richer <>, Mike Jones <>
Message-ID: <>
In-Reply-To: <>
References: <>
MIME-Version: 1.0
Content-Type: multipart/alternative; boundary="----=_Part_4963459_453117845.1452713808568"
Archived-At: <>
Cc: "<>" <>
Subject: Re: [OAUTH-WG] Mix-Up About The Mix-Up Mitigation
X-Mailman-Version: 2.1.15
Precedence: list
Reply-To: Bill Mills <>
List-Id: OAUTH WG <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Wed, 13 Jan 2016 19:36:52 -0000

Maybe this has been covered elsewhere, but one can see the case where "iss" in an example is set to "my_auth_server" and that cut/paste gets re-used.   That's also possible even in the OpenID Discovery mechanism, it requires the implementer to actually pick a unique value.  It would be better if this were not dependent on by-hand configuration.

    On Tuesday, January 12, 2016 8:03 PM, Justin Richer <> wrote:

 +1 to Brian’s point, and points to Mike for promising to address this. I wasn’t able to attend the meeting in Darmstadt, but I’ve been following the discussion and original papers. Let’s take this one piece at a time and not overreach with a solution.
In particular, the whole “late binding discovery” bit would cause huge problems on its own. There’s good reason that OpenID Connect mandates that the “iss” value returned from the discovery endpoint MUST be the same as the “iss” value coming back from the ID Token, so let’s not ignore that.
 — Justin

On Jan 12, 2016, at 5:53 PM, Mike Jones <> wrote:

John Bradley and I went over this today and I'm already planning on simplifying the draft along the lines described. I would have written this earlier but I've been busy at a NIST meeting today.

John has also stated writing a note about how cut-and-paste does and doesn't apply here but hasn't finished it yet because he's been similarly occupied.  He's also started writing up the state_hash token request parameter, as he agreed to do.

Watch this space for the new draft...

Best wishes,
-- MikeFrom:Brian Campbell
Sent:‎1/‎12/‎2016 5:24 PM
Subject:[OAUTH-WG] Mix-Up About The Mix-Up Mitigation

The "IdP Mix-Up" and "Malicious Endpoint" attacks (as well as variations on them) take advantage of the fact that there's nothing in the OAuth authorization response to the client's redirect_uri that identifies the authorization server. As a result, a variety of techniques can be used to trick the client into sending the code (or token in some cases) to the wrong endpoint.

To the best of my recollection the general consensus coming out of the meetings in Darmstadt (which Hannes mentioned inOAuth Security Advisory: Authorization Server Mix-Up) was to put forth an I-D as a simple extension to OAuth, which described how to return an issuer identifier for the authorization server and client identifier as authorization response parameters from the authorization endpoint. Doing so enables the client to know which AS the response came from and thus avoid sending the code to a different AS. Also, it doesn't introduce application/message level cryptography requirements on client implementations.

The mitigation draft that was posted yesterday diverges considerably from that with a significantly expanded scope that introduces OpenID Connect ID Tokens (sort of anyway) to regular OAuth and the retrieval of a metadata/discovery document in-between the authorization request and the access token request.

It is possible that my recollection from Darmstadt is wrong. But I expect others who were there could corroborate my account of what transpired. Of course, the agreements out of the Darmstadt meeting were never intended to be the final word - the whole WG would have the opportunity to weigh, as is now the case. However, a goal of meeting face-to-face was to come away with a good consensus towards a proposed solution that could (hopefully) be implementable in the very near term and move thought the IETF process in an expedited manner. I believe we'd reached consensus but the content of -00 draft does not reflect it.

I've made the plea off-list several times to simplify the draft to reflect the simple solution and now I'm doing the same on-list. Simplify the response validation to just say not to send the code/token back to an AS entity other that the one identified by the 'iss' in the response. And remove the id_token and JWT parts that . 

If this WG and/or the larger community believes that OAuth needs signed responses, let's develop a proper singed response mechanism. I don't know if it's needed or not but I do know that it's a decent chunk of work that should be conscientiously undertaken independent of what can and should be a simple to understand and implement fix for the idp mix-up problem.

OAuth mailing list

OAuth mailing list