[Openid-specs-ab] Defining a Hardened (Mix-up and Cut-and-Paste Proof) OpenID Connect Profile

William Denniss wdenniss at google.com
Tue Apr 12 20:58:01 UTC 2016


On Tue, Apr 12, 2016 at 12:50 PM, Hans Zandbelt <hzandbelt at pingidentity.com>
wrote:

> from an implementers/deployment standpoint I would argue that if the
> id_token is delivered in the front channel, I may just as well get the
> access token from there too rather than having to deal with the overhead of
> calling the token endpoint, esp. since at_hash is there to protect integrity
>
> so I'd favor response_mode=form_post, response_type="id_token token" over
> hybrid
>
> I realize that this doesn't leverage the possibility of using a client
> secret to get the access token but it doesn't really seem to matter
> security-wise at this point as the id_token was delivered without
> leveraging it as well
>
> anything wrong with that line of reasoning?
>

1) Server won't have offline access with "id_token token". 2) The primary
case we are dealing with today is the code flow, and we are really just
suggesting clients add security checks onto their existing flows by
leveraging id_token.

It's true that you could do many of the same checks with "id_token token"
to verify that the access token was issued by the correct party and avoid
cut-and-paste and mix-up, if you only needed a once-off access token.

You raise an interesting point regarding client confidentiality.


> On 4/12/16 9:23 PM, William Denniss wrote:
>
>> Good point.
>>
>> Regarding the OP tests, the following are relevant to mitigate the
>> cut-and-paste and mix-up attacks:
>>
>>  1. ID Token has nonce when requested for code flow [Basic]
>> (OP-nonce-code)
>>  2. Request with response_mode=form_post [Extra] (OP-Response-form_post)
>>
>> 1) is important for preventing cut-and-paste (the id token needs to
>> contain the 'nonce')
>> 2) is important for preventing mix-up as it means the redirect endpoint
>> gets the id_token on the response at the server, as opposed to in the
>> URI fragment.
>>
>> Unfortunately, form_post is optional for OPs, and sending the nonce on
>> the code flow is optional for RPs (though fortunately to it is
>> compulsory for OPs to support thanks to OP-nonce-code).
>>
>> We could add an hardened OP test for:
>> – Forcing nonce to be present on the code flow
>>
>> We should definitely have RP tests for:
>> – sending and validating nonce on the code flow
>> – validating the c_hash, iss, aud on the hybrid flow
>>
>> How we would profile these tests I'm not sure; would they go in the
>> Basic testing profile, or in a new Hardened one?  We could move
>> OP-Response-form_post to the Basic profile if we wanted to be
>> opinionated, or define a new profile.
>>
>> The good news is that supporting the features required to mitigate
>> mix-up & cut-and-paste is not all that hard to do in Connect.
>>
>>
>> On Tue, Apr 12, 2016 at 10:46 AM, Nick Roy <nroy at internet2.edu
>> <mailto:nroy at internet2.edu>> wrote:
>>
>>     Would it be possible to check for the secure behavior in Roland's
>>     test suite and either not certify non-mitigating implementations, or
>>     offer a risk mitigation add-on cert for those that do the right thing?
>>
>>     Nick
>>
>>     From: Openid-specs-ab <openid-specs-ab-bounces at lists.openid.net
>>     <mailto:openid-specs-ab-bounces at lists.openid.net>> on behalf of
>>     William Denniss <wdenniss at google.com <mailto:wdenniss at google.com>>
>>     Date: Tuesday, April 12, 2016 at 11:01 AM
>>     To: "openid-specs-ab at lists.openid.net
>>     <mailto:openid-specs-ab at lists.openid.net>"
>>     <openid-specs-ab at lists.openid.net
>>     <mailto:openid-specs-ab at lists.openid.net>>
>>     Subject: [Openid-specs-ab] Defining a Hardened (Mix-up and
>>     Cut-and-Paste Proof) OpenID Connect Profile
>>
>>     One item that came out of the discussions on the sidelines of IETF95
>>     with folk from this WG (specifically Nat, Mike, John, Brian and
>>     myself) was the need for the Connect community to respond to the
>>     recently <http://arxiv.org/abs/1508.04324v2/> documented
>>     <http://arxiv.org/abs/1601.01229v2/> security threats.
>>
>>     Connect is actually in a much stronger place for mitigating these
>>     attacks (as noted in the papers themselves) than pure OAuth, with
>>     the id_token offering a cryptographic binding of the code to the
>>     issuer, audience and session identifier (nonce).
>>
>>     However, certain steps need to be followed, for example using
>>     'nonce' with the code flow (which is optional to implement for
>>     clients) to protect against cut-and-paste, and using the form-post
>>     response type with the hybrid flow to verify that the code was
>>     issued by the expected IdP, to ensure the code is exchanged at the
>>     correct token endpoint (mitigating mix-up).
>>
>>     We discussed last week creating a profile of Connect that recommends
>>     those practices to mitigate these classes of attack as a response to
>>     the security researchers' findings. I wanted to share that
>>     suggestion with the list, and continue the conversation.
>>
>>
>>
>>
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>>
>>
> --
> Hans Zandbelt              | Sr. Technical Architect
> hzandbelt at pingidentity.com | Ping Identity
>
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