Re: [kitten] [nfsv4] rpcsec-gssv3 multi-principal authentication

[Nico Williams <[e-mail]>]

On Wed, Sep 3, 2014 at 12:47 PM, J. Bruce Fields <[e-mail]> wrote:
> Sorry, I haven't been thinking about this, I'm probably confused, but I
> think I was imagining an attack something like:
>
>         - I, a rogue client, sniff some random krb5 traffic from the
>           user.
>         - That traffic includes at least one (rpc header, mic of rpc
>           header) pair.
>         - I send a CREATE call using that rpc header as the nonce data.
>
> ?

It almost works, but remember, the server must have the security
context to verify the MIC with, and that context will have to be tied
to the same NFSv4 client ID (same session).

Oh, but maybe some servers have a global RPCSEC_GSS context handle?
If so, that would be a problem.  In that case the server could pick
the nonce.  Or the MIC could be taken over more content (e.g., also a
MIC made with the client context).  Just in case, this would be a good
change to make.

Nico
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