[openssl-dev] [openssl.org #3712] TLS Renegotiation with Java is broken

[Hubert Kario via RT]

On Friday 16 October 2015 08:53:06 Matt Caswell via RT wrote:
> On 13/10/15 12:31, Hubert Kario via RT wrote:
> > On Tuesday 13 October 2015 09:22:53 Matt Caswell via RT wrote:
> >> On 12/10/15 17:19, Matt Caswell via RT wrote:
> >>> On 12/10/15 16:39, Matt Caswell via RT wrote:
> >>>> The value of "in_read_app_data" not being true when it is
> >>>> supposed
> >>>> to
> >>>> appears to be running into a slightly different bug. It's also
> >>>> present in 1.0.2 but you have to switch off version negotiation.
> >>>> So running s_server like this in 1.0.2 and rerunning Hubert's
> >>>> test
> >>>> will hit it:
> >>>> 
> >>>> openssl s_server -www -tls1_2
> >>>> 
> >>>> The 1.0.2 version negotiation is hiding the issue. In master
> >>>> version neg has been completely rewritten and simplified - but in
> >>>> doing so no longer hides the problem. :-(
> >>> 
> >>> Having done some more digging it seems the problem only occurs if
> >>> you
> >>> get the initial handshake, following by a second reneg handshake
> >>> *and* interleaved app data all within the scope of a *single*
> >>> SSL_read call. AFAICT if SSL_read returns between the first
> >>> handshake and the second, you don't get the problem.
> >> 
> >> Ok, updated version of the patch attached. This is for 1.0.2 but
> >> should pass Hubert's tests even when you run s_server with
> >> "-tls1_2".
> > 
> > yup, looks good with -tls1_2 now too
> > 
> > for some reason my side can't negotiate TLS 1.1 or TLS 1.0 correctly
> > so can't test -tls1_1 or -tls1 (I'm likely generating malformed CKE
> > there, but need to check to be sure)
> 
> I raised the ambiguity in the spec about when in the handshake
> interleaved app data is allowed with the TLS WG. You can see the
> thread here:
> https://www.ietf.org/mail-archive/web/tls/current/threads.html#18017
> 
> I got a few responses, not all of which were consistent, and giving
> different views. To summarise what I interpret as the main points:
> 
> 1) Where a view was given it seemed to concur with the views expressed
> here that the most sensible interpretation of the spec wording is
> that interleaved app data is allowed up until the CCS, but not
> between CCS and Finished.
> 2) There was also a view expressed that, regardless of what the spec
> says, allowing interleaved app data is *dangerous*!
> 3) There seemed to be differing views on just how dangerous ranging
> from it being "a highly dangerous idea" to "...there is a need for
> caution, but in reality, it's not like you can use renegotiation to
> hand-off to someone else entirely.  The person you are talking to
> hasn't changed. What is dangerous is making assertions about *new*
> things that the renegotiation introduces", although the same person
> who made that last observation also provided a list of very onerous
> mitigations that we should put in place if were to do it (none of
> which are likely to be adopted IMO without some form of official
> advice from the TLS WG).
> 
> So now I really don't know what the "right" way forward is. Should we
> be applying the patch or not?

I can't think of a way to exploit it if two assumptions hold:
 1). we have secure renegotiation
 2). API calls return metadata (certificates especially) from *active* 
     context, not one currently negotiated

-- 
Regards,
Hubert Kario
Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: not available
URL: <http://mta.openssl.org/pipermail/openssl-dev/attachments/20151016/ce7f7b43/attachment.sig>