Re: [TLS] Dnsdir early review of draft-ietf-tls-svcb-ech-01

Do we want a few sentences in Security Considerations that references
https://www.rfc-editor.org/rfc/rfc9460.html#section-3.1 to call this out?

This seems like something that became less clear when we split these two
docs apart.
Most of draft-ietf-tls-svcb-ech used to be a section of what is now rfc9460
but got split out
due to publication timelines.  It may be that some non-normative references
back to rfc9460
might help readers not miss things like this which might have been more
clear when they
were a single document.

   Erik

On Fri, Mar 29, 2024 at 11:31 PM Ted Lemon <mellon@fugue.com> wrote:

> Yes, that fully addresses my concern. Thanks!
>
> Op vr 29 mrt 2024 om 22:54 schreef Eric Rescorla <ekr@rtfm.com>
>
>>
>> Hi Ted,
>>
>> Doesn't this section of RFC 9460 address this case and say what you are
>> recommending:
>>
>> https://www.rfc-editor.org/rfc/rfc9460.html#section-3.1
>>
>> -Ekr
>>
>>
>>
>> On Fri, Mar 29, 2024 at 6:49 PM Ted Lemon <mellon@fugue.com> wrote:
>>
>>> Okay, I think I see the disconnect, maybe. The issue I'm pointing to is
>>> that you may or may not be doing DNSSEC validation. And you may or may not
>>> be /able/ to do DNSSEC validation if the infrastructure breaks it
>>> accidentally or deliberately.
>>>
>>> The document says: "The SVCB-optional client behavior specified in
>>> (Section 3 of [SVCB]) permits clients to fall back to a direct connection
>>> if all SVCB options fail. This behavior is not suitable for ECH, because
>>> fallback would negate the privacy benefits of ECH."
>>>
>>> So it's saying that the default handling of SVCB is incorrect and would
>>> fail open, and overriding that behavior. Given that this is the case, that
>>> implies that it matters whether the data has been validated, but nowhere in
>>> the document, certainly not in Security Considerations, is any mention made
>>> of this issue. So that's what I'm pointing out.
>>>
>>> It is absolutely not the case in practice that all stub resolvers do
>>> validation. You are making a security decision about trust based on data
>>> the trustworthiness of which you've not discussed, in a situation where the
>>> implementor has meaningful choices to make with respect to validating that
>>> trustworthiness. So it's worth mentioning that if the policy is not to
>>> validate, this vulnerability exists.
>>>
>>> I'm a DNS guy, not a TLS guy, so I don't know the history of this
>>> work—I'm just making this observation about the document I was asked to
>>> review. The fact that (apparently) no DNSDIR review ever raised this issue
>>> about the other documents you mentioned is of no interest to me—I'm not
>>> reviewing those documents.Whether you take this advice is between you and
>>> the IESG. I'm not even claiming to be right—just pointing out the issue I
>>> see.
>>>
>>> On Fri, Mar 29, 2024 at 7:21 PM Rob Sayre <sayrer@gmail.com> wrote:
>>>
>>>> I don't think it relates to DNSSEC. You can fail at DNS (DNSSEC
>>>> failure) or you can fail during ECH (unless you want to use non-ECH, which
>>>> is not ECH, and not part of this draft).
>>>>
>>>> It makes sense to me: one can reject a request unless the requirements
>>>> embedded in the SVCB are met (the server chooses those, which can include
>>>> many aspects of the request). I don't understand why one would insert
>>>> DNSSEC here. That seems to be the whole point--it works without it.
>>>>
>>>> thanks,
>>>> Rob
>>>>
>>>>
>>>> On Fri, Mar 29, 2024 at 3:57 PM Ted Lemon <mellon@fugue.com> wrote:
>>>>
>>>>> I'm not telling you that you have to require DNSSEC. I'm saying the
>>>>> document is incomplete if you don't talk about how it relates to DNSSEC. I
>>>>> think EKR got the point, so maybe go with his approach?
>>>>>
>>>>> On Fri, Mar 29, 2024 at 6:27 PM Rob Sayre <sayrer@gmail.com> wrote:
>>>>>
>>>>>> It's a policy choice, though, right? I think ekr hinted at this issue
>>>>>> as well.
>>>>>>
>>>>>> It's that one might also view requests that reveal the SNI as
>>>>>> insecure. If that's the case, DNSSEC doesn't help. There will certainly be
>>>>>> a transition period where that will be impractical for many servers. I
>>>>>> think these are separate problems, though.
>>>>>>
>>>>>> thanks,
>>>>>> Rob
>>>>>>
>>>>>>
>>>>>> On Fri, Mar 29, 2024 at 3:10 PM Ted Lemon <mellon@fugue.com> wrote:
>>>>>>
>>>>>>> It looks like if you can't get the SCVB you're going to fail
>>>>>>> insecure, so being able to use DNSSEC to prevent that for signed domains
>>>>>>> seems worthwhile.
>>>>>>>
>>>>>>> On Fri, Mar 29, 2024 at 4:41 PM Rob Sayre <sayrer@gmail.com> wrote:
>>>>>>>
>>>>>>>> On Fri, Mar 29, 2024 at 1:02 PM Ted Lemon via Datatracker <
>>>>>>>> noreply@ietf.org> wrote:
>>>>>>>>
>>>>>>>>>
>>>>>>>>> I don't think it's reasonable to specify the privacy properties of
>>>>>>>>> SVCB and
>>>>>>>>> /not/ talk about DNSSEC validation.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Could you explain more about this part? I think DNSSEC doesn't add
>>>>>>>> much here, unless you want to accept non-ECH traffic. For example, many of
>>>>>>>> the test servers will bounce you to some other site if you don't send ECH
>>>>>>>> or screw it up in some way (speaking as someone who has screwed it up many
>>>>>>>> times...).
>>>>>>>>
>>>>>>>> I think there might be a DoS attack here, where someone messes with
>>>>>>>> the response, but they can also turn off the DNSSEC bit unless it's
>>>>>>>> DoT/DoH/DoQ etc. So, if using those, it's just the trustworthiness of the
>>>>>>>> DNS server itself, right? Sorry if I'm missing something.
>>>>>>>>
>>>>>>>> thanks,
>>>>>>>> Rob
>>>>>>>>
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