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

[Ted Lemon <[e-mail]>]

Yes, that fully addresses my concern. Thanks!

Op vr 29 mrt 2024 om 22:54 schreef Eric Rescorla <[e-mail]>

>
> 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 <[e-mail]> 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 <[e-mail]> 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 <[e-mail]> 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 <[e-mail]> 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 <[e-mail]> 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 <[e-mail]> wrote:
>>>>>>
>>>>>>> On Fri, Mar 29, 2024 at 1:02 PM Ted Lemon via Datatracker <
>>>>>>> [e-mail]> 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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