Re: [DNSOP] Validating responses when following unsigned CNAME chains...

Shumon Huque <shuque@gmail.com> Fri, 01 May 2020 11:41 UTC

Return-Path: <shuque@gmail.com>
X-Original-To: dnsop@ietfa.amsl.com
Delivered-To: dnsop@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id BDBAF3A1041 for <dnsop@ietfa.amsl.com>; Fri, 1 May 2020 04:41:27 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.097
X-Spam-Level:
X-Spam-Status: No, score=-2.097 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, HTML_MESSAGE=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id KuidhIU8pQ-c for <dnsop@ietfa.amsl.com>; Fri, 1 May 2020 04:41:26 -0700 (PDT)
Received: from mail-ed1-x52c.google.com (mail-ed1-x52c.google.com [IPv6:2a00:1450:4864:20::52c]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 698683A1023 for <dnsop@ietf.org>; Fri, 1 May 2020 04:41:24 -0700 (PDT)
Received: by mail-ed1-x52c.google.com with SMTP id r7so7039718edo.11 for <dnsop@ietf.org>; Fri, 01 May 2020 04:41:24 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=1HEpVQmTCMrCH/a1Gn55TtQRbTPy24UqyFMtZ/lHXQ0=; b=WrjIciYAYoOdE0SWmaIU7Ih/GOoGa1Dt8KEL1ysynEuREfvs8dA8+EkvuY90cpMROL zTetHdQDfKf5XRJVWHSJvwpi827j0QeMHDUFguCgq3qzEkDnE5lZScXOj9bZXccchXHL Q3ddakXruVeP6v1+br6l6yb5API+pzDtnW8tWfcaie84g8QrhYplaffhMjOVqNgbG8r0 W/6ziOuTKfGtCH6Ig0xbUu6xsmtYTTev8auMrAnOQzGR9rmDKuMxscxbBRRvt37tRoI7 rgj7w/ecu3L71KlxsCYYtDjBOR8SihSN7s3r9/vKpbsIm4dauxLQlV5foBVdLMMpdj5W 3wGA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=1HEpVQmTCMrCH/a1Gn55TtQRbTPy24UqyFMtZ/lHXQ0=; b=iNoTubaybgtlHOPBb8CzUZ75IRj3laq7wb0XCPRZDEbjPeiaPSlBo03p66zxNY2n9b V/yerYk2XOM2F6H4VM+Zen8yUir88atva/t7ksuumEBQ3OKzWJPb9GOvXM1e7CdGIFBy H/dlvv9aPjUtHl61ZyDBMOkNWHqcTYjw3soRnkXHv6cMDZJFDpLnQsQk4QwWc4EDfjFW 52DFkoecDSvVUdl9e2aJun6Dhf9g/rvpE7bmnCyCeXjnTm2hXf1Ok2gdLH7RQEzp0HRJ uqrUrdkwprcNyjDg8cc9t4j+QHorPdVjchShumRQCSDISi03wbDgzgC9lW6mopdG1NeS rvFQ==
X-Gm-Message-State: AGi0PuZUVl57m1Mrfn6xW4v6D2lN0YfI7wABQRmrWTbwy7jWkJfaFMQg xXVHW1nnB9K0IGXYqPvYj0OI52G9yjKEWNTV6AThHkta
X-Google-Smtp-Source: APiQypJu3QEerGMoh+jANkyTivAwkScZhcvidnfIHhA2wkP5bVUjHTde1MfyBRiMr5T4TX1OvPvf2KkNEZKZkUpP9TA=
X-Received: by 2002:aa7:d783:: with SMTP id s3mr3227647edq.64.1588333282392; Fri, 01 May 2020 04:41:22 -0700 (PDT)
MIME-Version: 1.0
References: <1EA6A13C-6E60-4ED9-9A50-E33D9D17504C@fugue.com> <129b0546-0123-30e0-cfca-8a66721ab046@nthpermutation.com> <6311BB51-4617-4316-A56D-EEA73A42D4A0@fugue.com> <e085e747-21f3-145e-2613-81c2a144ede6@nthpermutation.com> <2F9A828C-FC80-498D-B8C2-3DC804D75B0E@fugue.com>
In-Reply-To: <2F9A828C-FC80-498D-B8C2-3DC804D75B0E@fugue.com>
From: Shumon Huque <shuque@gmail.com>
Date: Fri, 1 May 2020 07:41:11 -0400
Message-ID: <CAHPuVdVcN7dF3KwsKaP2UhpSFS9YFkMcdhZpWqixVQK8KPNGng@mail.gmail.com>
To: Ted Lemon <mellon@fugue.com>
Cc: Michael StJohns <msj@nthpermutation.com>, "dnsop@ietf.org WG" <dnsop@ietf.org>
Content-Type: multipart/alternative; boundary="00000000000015016405a494a9bc"
Archived-At: <https://mailarchive.ietf.org/arch/msg/dnsop/yUk194Csm4kRPxYLkFg54Qq1jHI>
Subject: Re: [DNSOP] Validating responses when following unsigned CNAME chains...
X-BeenThere: dnsop@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: IETF DNSOP WG mailing list <dnsop.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/dnsop>, <mailto:dnsop-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/dnsop/>
List-Post: <mailto:dnsop@ietf.org>
List-Help: <mailto:dnsop-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/dnsop>, <mailto:dnsop-request@ietf.org?subject=subscribe>
X-List-Received-Date: Fri, 01 May 2020 11:41:28 -0000

On Thu, Apr 30, 2020 at 2:47 PM Ted Lemon <mellon@fugue.com> wrote:

> On Apr 30, 2020, at 2:31 PM, Michael StJohns <msj@nthpermutation.com>
> wrote:
>
> Because an attacker can twiddle with a CNAME.  So while the recipient sees
> a CNAME pointing at a validatable end item, that may not have been the end
> name the publisher provided.   I'd probably say unsecure though, as I don't
> expect the client can detect bogus in this case unless there was a rule
> saying this was a bogus configuration.
>
> Mike
>
> ps - What's the validation level for a secured CNAME that points at an
> unsecured CNAME that points to a secured A record?
>
> I think that what we’re really talking about is that we have some chain of
> items where some items are provably not signed, and some are provably
> signed and have been validated. Any items that do not match one of these
> two criteria can be treated as “unknown.”  So:
>
> * If _all_ the items are provably signed and have been validated, the
> answer sets the AD bit.
>

yes.


> * If _some_ of the items have been validated, and others are provably not
> signed, then the answer doesn’t set the AD bit, but an answer is sent.
>

yes.


> * If we have a partial answer because we didn’t get some answers, is that
> any different than the case where we got bogus answers?
>

Depending on what we didn't get, this answer would be Bogus or
Indeterminate, per RFC 4035, Section 4.3. I think the practical effect of
this is the same for any client of the resolver: SERVFAIL (or if client set
checking disabled, return the partial answers with AD=0,CD=1).

Shumon.