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
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