Re: [OAUTH-WG] Benjamin Kaduk's No Objection on draft-ietf-oauth-jwsreq-26: (with COMMENT)

[Vladimir Dzhuvinov <[e-mail]>]

+1 to make the "typ" check, as Filip suggested, normative, as existing
client and RP deployments with undefined "typ" will not be affected. New
deployments should be encouraged to type the JWT, and thus be made safer.


Regarding the "sub != client_id" check -- could a simple rejection of
all JWTs with "sub" present suffice?

I find it difficult to imagine what else a client could end up setting
the "sub" claim to, if it does end up populating it for some reason.

Rejecting JWTs with "sub=client_id" or "sub" present will break
deployments where a client for some reason sets the "typical" JWT
claims, and "sub" is a typical one, but if those deployments happen to
accept client_secret_jwt or private_key_jwt client authentication, they
could well be vulnerable to cross-JWT confusion attacks.


Vladimir

On 14/08/2020 13:58, Filip Skokan wrote:
> Hi Mike, Nat,
>
> I thought we would go as far as making these normative requirements
>
>   * if the Request Object includes a sub claim with the value of the
>     client_id the AS MUST reject the request
>   * if the Request Object is explicitly typed (typ) its value MUST be ...
>
> First rejects client assertions to be passed as Request Objects.
> Second rejects all future typed JWT profiles from being used as
> Request Objects without worrying about the claims they may or may not
> contain.
>
> Or is that breaking?
>
> S pozdravem,
> *Filip Skokan*
>
>
> On Fri, 14 Aug 2020 at 00:59, Mike Jones
> <Michael.Jones=[e-mail]
> <mailto:[e-mail]>> wrote:
>
>     At Nat's request, I've created a pull request addressing Cross-JWT
>     Confusion security considerations.  It addresses both Brian's
>     comment and the IESG comments about explicit typing.  See the full
>     PR at https://bitbucket.org/Nat/oauth-jwsreq/pull-requests/10. 
>     See the source diffs at
>     https://bitbucket.org/Nat/oauth-jwsreq/pull-requests/10/address-iesg-and-working-group-comments/diff#chg-draft-ietf-oauth-jwsreq.xml. 
>     Please review!
>
>     This is only the first commit, albeit, one that addresses some of
>     the must substantive issues.  More commits will follow addressing
>     additional IESG comments.
>
>                                     -- Mike
>
>     -----Original Message-----
>     From: OAuth <[e-mail]
>     <mailto:[e-mail]>> On Behalf Of Benjamin Kaduk
>     Sent: Thursday, August 13, 2020 2:59 PM
>     To: Brian Campbell <[e-mail]
>     <mailto:[e-mail]>>
>     Cc: [e-mail]
>     <mailto:[e-mail]>; [e-mail]
>     <mailto:[e-mail]>; The IESG <[e-mail]
>     <mailto:[e-mail]>>; oauth <[e-mail]
>     <mailto:[e-mail]>>
>     Subject: Re: [OAUTH-WG] Benjamin Kaduk's No Objection on
>     draft-ietf-oauth-jwsreq-26: (with COMMENT)
>
>     Oops, that's my bad.  Thanks for the correction -- I've linked to
>     your message in the datatracker (but didn't bother to have the
>     datatracker send a third copy of my updated-again ballot position).
>
>     -Ben
>
>     On Thu, Aug 13, 2020 at 03:00:33PM -0600, Brian Campbell wrote:
>     > While some discussion of why explicit typing was not used might be
>     > useful to have, that thread started with a request for security
>     > considerations prohibiting use of the "sub" with a client ID value.
>     > Because such a request JWT could be repurposed for JWT client
>     > authentication. And explicit typing wouldn't help in that situation.
>     >
>     > On Tue, Aug 11, 2020 at 2:50 PM Benjamin Kaduk via Datatracker <
>     > [e-mail] <mailto:[e-mail]>> wrote:
>     >
>     > >
>     > >
>     --------------------------------------------------------------------
>     > > --
>     > > COMMENT:
>     > >
>     --------------------------------------------------------------------
>     > > --
>     > >
>     > > [updated to note that, per
>     > >
>     https://mailarchive.ietf.org/arch/msg/oauth/Lqu15MJikyZrXZo5qsTPK2o0
>     > > eaE/ and the JWT BCP (RFC 8725), some discussion of why explicit
>     > > typing is not used would be in order]
>     > >
>     > >
>     >
>     > --
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-- 
Vladimir Dzhuvinov