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Re: [nfsv4] RPCSEC_GSS analysis (was Re: [secdir] SECDIR Review of draft-ietf-nfsv4-umask-03)

Nico Williams <nico@cryptonector.com> Mon, 05 June 2017 17:30 UTC

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Date: Mon, 05 Jun 2017 12:30:19 -0500
From: Nico Williams <nico@cryptonector.com>
To: Watson Ladd <watsonbladd@gmail.com>
Cc: Phillip Hallam-Baker <phill@hallambaker.com>, Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com>, NFSv4 <nfsv4@ietf.org>, "secdir@ietf.org" <secdir@ietf.org>
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Subject: Re: [nfsv4] RPCSEC_GSS analysis (was Re: [secdir] SECDIR Review of draft-ietf-nfsv4-umask-03)
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The biggest security problem with RPCSEC_GSS in general, and NFSv4 in
particular, is that RPC protocols like NFSv4 are generally three-party
protocols, not two-party protocols, but RPCSEC_GSS uses a two-party
security protocol (GSS) and does not compose use of it to construct a
three-party protocol.

The parties are: the client, the users on the client, and the server.

The client / user distinction is usually important and real: the client
is the OS, which does not necessarily (and usually does NOT) trust the
user.

This leads to some interesting attacks!

RPCSEC_GSSv3 adds the missing composition of GSS into a three-party
model.

Nico
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