Re: [Gen-art] Gen-art Telechat review of draft-ietf-nfsv4-rpcsec-gssv3-15
Elwyn Davies <elwynd@dial.pipex.com> Fri, 22 January 2016 16:19 UTC
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To: "Adamson, Andy" <William.Adamson@netapp.com>
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From: Elwyn Davies <elwynd@dial.pipex.com>
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Date: Fri, 22 Jan 2016 16:18:48 +0000
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Cc: General area reviewing team <gen-art@ietf.org>, Tom Haynes <thomas.haynes@primarydata.com>, "draft-ietf-nfsv4-rpcsec-gssv3.all@ietf.org" <draft-ietf-nfsv4-rpcsec-gssv3.all@ietf.org>
Subject: Re: [Gen-art] Gen-art Telechat review of draft-ietf-nfsv4-rpcsec-gssv3-15
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Hi, Andy. Thanks for the update. Version 16 is fine by me - all done. As regards minorversion2, I'm afraid I misunderstood the implications (or otherwise) of the discussions of multiple principals. As you say, minorversion2 doesn't use the multiprincipal option. Regards, Elwyn On 20/01/2016 19:49, Adamson, Andy wrote: >> 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 >>> -- >>
- [Gen-art] Gen-art Telechat review of draft-ietf-n… Elwyn Davies
- Re: [Gen-art] Gen-art Telechat review of draft-ie… Adamson, Andy
- Re: [Gen-art] Gen-art Telechat review of draft-ie… Martin Stiemerling
- Re: [Gen-art] Gen-art Telechat review of draft-ie… Adamson, Andy
- Re: [Gen-art] Gen-art Telechat review of draft-ie… Elwyn Davies
- Re: [Gen-art] Gen-art Telechat review of draft-ie… Adamson, Andy