Re: [Gen-art] Gen-art Telechat review of draft-ietf-nfsv4-rpcsec-gssv3-15

"Adamson, Andy" <William.Adamson@netapp.com> Wed, 20 January 2016 19:49 UTC

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From: "Adamson, Andy" <William.Adamson@netapp.com>
To: Elwyn Davies <elwynd@dial.pipex.com>
Thread-Topic: Gen-art Telechat review of draft-ietf-nfsv4-rpcsec-gssv3-15
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Date: Wed, 20 Jan 2016 19:49:26 +0000
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Subject: Re: [Gen-art] Gen-art Telechat review of draft-ietf-nfsv4-rpcsec-gssv3-15
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> On Jan 16, 2016, at 1:15 PM, Elwyn Davies <elwynd@dial.pipex.com> wrote:
> 
> I am the assigned Gen-ART reviewer for this draft. The General Area
> Review Team (Gen-ART) reviews all IETF documents being processed
> by the IESG for the IETF Chair. Please wait for direction from your
> document shepherd or AD before posting a new version of the draft.
> 
> For more information, please see the FAQ at
> 
> <http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.
> 
> Document: draft-ietf-nfsv4-rpcsec-gssv3-15.txt
> Reviewer: Elwyn Davies
> Review Date: 2016/01/16
> IETF LC End Date: 2015/12/09
> IESG Telechat date: 2016/01/21

Hi Elwyn

Where can I find the telechat details (time off call and phone #)?


> 
> Summary: Almost ready.  Thank you for addressing my comments from the last call review.  For the record there are a couple of other points that have been raised elsewhere that need to be addressed.
> 
> Major issues:
> s2.7.1/s4: There is a security issue with RPCSEC_GSS_CREATE when multi-principal authentication is required.  See mail [1] below. This may have a (minor) knock-on effect of the NFSv4.2 specification where this is used; as currently specified (draft-ietf-nfsv4-minorversion2-40) use of privacy is already mandated for at least some of the relevant uses of RPCSEC_GSS_CREATE in NFSv4.2 which will mitigate the problem.  I have raised this issue in the Telechat review of the NFSv4.2 draft to ensure that privacy is mandated in *all* relevant cases - and to ensure changes are coordinated.

NFSv4.2 does not use the multi-principal assertion.

—>Andy

> 
> Minor issues:
> s2.7.1.4: Some refinement of the constraints on the rp_name string marked as 'human readable' would be desirable.
> 
> Nits/editorial comments:
> None
> 
> ========================================
> [1]
> > From: Nico Williams <nico@cryptonector.com>
> > Subject: Re: rpcsec-gssv3
> > Date: January 11, 2016 at 8:01:52 PM EST
> > To: Benjamin Kaduk <kaduk@mit.edu>
> > Cc: Stephen Farrell <stephen.farrell@cs.tcd.ie>, "sec-ads@ietf.org" <sec-ads@ietf.org>, Spencer Dawkins <spencerdawkins.ietf@gmail.com>, Martin Stiemerling <mls.ietf@gmail.com>, "Adamson, Andy" <William.Adamson@netapp.com>
> >
> > On Thu, Jan 07, 2016 at 02:14:01PM -0600, Nico Williams wrote:
> >> Ok, thanks.  I'll post a write up this Saturday.
> >
> > Or on Monday.
> >
> > OK, so, a while back Ben Kaduk noticed that there is a security problem
> > with the RPCSEC_GSS_CREATE procedure with multi-principal
> > authentication.
> >
> > The attack varies from easy to difficult to mount depending on whether
> > the server implements a global or per-connection GSS context handle
> > namespace, and whether it assigns them in a way that the attacker can
> > get a specific context handle number assigned to it.
> >
> > There are two fixes, the simplest of which is to require that the
> > RPCSEC_GSS_CREATE procedure be called with privacy protection when using
> > the multi-principal authentication feature.
> >
> > To recap how the RPCSEC_GSS_CREATE procedure with multi-principal
> > authentication feature works, the client first makes a MIC token with a
> > GSS context that authenticates the user to the server, then it it uses
> > that MIC in the payload of the RPCSEC_GSS_CREATE procedure. The
> > RPCSEC_GSS_CREATE procedure is itself protected with a GSS context that
> > authenticates the client.
> >
> > The problem is that the data that the user GSS context MICs is
> > insufficiently strong a statement of intent because it only identifies
> > the client host GSS context by its RPCSEC_GSS context handle ID and
> > nothing more.  An attacker that can intercept an RPCSEC_GSS_CREATE
> > procedure and cause the RPCSEC_GSS context handle to get re-assigned
> > will be able to steal the victim's identity.
> >
> > There are a number of solid fixes that fall into two classes:
> >
> > 1) Add to the data that the user context MICs in order to improve the
> >   quality of the statement of intent.
> >
> >   E.g., add the client host principal's name.  Or add a MIC made with
> >   the client host's GSS context.
> >
> > 2) Make it so the attacker cannot steal the MIC made with the user GSS
> >   context.
> >
> >   E.g., use privacy protection for the RPCSEC_GSS_CREATE procedure,
> >   thus the MIC made with the user GSS context cannot be obtained by the
> >   attacker without having the client host's or server's credentials.
> >   Stephen proposed this.
> >
> >   (The OpenAFS rxgk protocol uses GSS_Pseudo_random() [RFC4401] to
> >   similar effect.)
> >
> > At this stage the simplest thing to do is to require that clients always
> > use privacy protection for the RPCSEC_GSS_CREATE procedure. Note
> > that there is nothing that the server can do to prevent this attack if
> > clients don't use privacy protection for this, but the server should
> > still reject RPCSEC_GSS_CREATE procedure calls without privacy
> > protection.  (All of this is only for the multi-principal authentication
> > case.)
> >
> > Nico
> > --
> 
>