IETF Logo Mail Archive

Re: [ietf-smtp] MTS-STS validation when MX host points to a CNAME, violating RFC 2181 § 10.3

John Levine <johnl@taugh.com> Thu, 01 April 2021 00:30 UTC

Return-Path: <johnl@iecc.com>
X-Original-To: ietf-smtp@ietfa.amsl.com
Delivered-To: ietf-smtp@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 0DBEF3A3CE3 for <ietf-smtp@ietfa.amsl.com>; Wed, 31 Mar 2021 17:30:33 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.851
X-Spam-Level:
X-Spam-Status: No, score=-1.851 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, HEADER_FROM_DIFFERENT_DOMAINS=0.249, 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=iecc.com header.b=exgDvr6f; dkim=pass (2048-bit key) header.d=taugh.com header.b=vxDceQyG
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 GTgVXwBFQGbW for <ietf-smtp@ietfa.amsl.com>; Wed, 31 Mar 2021 17:30:27 -0700 (PDT)
Received: from gal.iecc.com (gal.iecc.com [IPv6:2001:470:1f07:1126:0:43:6f73:7461]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 802A33A3CE1 for <ietf-smtp@ietf.org>; Wed, 31 Mar 2021 17:30:27 -0700 (PDT)
Received: (qmail 74306 invoked from network); 1 Apr 2021 00:30:24 -0000
DKIM-Signature: v=1; a=rsa-sha256; c=simple; d=iecc.com; h=date:message-id:from:to:cc:subject:in-reply-to:mime-version:content-type:content-transfer-encoding:cleverness; s=12240.60651420.k2103; bh=zYEQXqyQCTPpxPQOEG+9kkcOxoLAyo1LpWPkilPw6e4=; b=exgDvr6fbS1ENTZoFXpLcdiDBI2ip7aPG8pep3JouNcoPYZSH4msoqURmf/mQ76RAw4neHsBCmIZe3exPBXcA2kX8vHRnuZaNFPi3/CCSayqkm/Qzo4iTOeuu3PP1po9qTuQbxhrrJZ1B5z9fl1JdTo0a2rWxzjr9lovadW6nYmvsKn72pLdu294+fLahUSbAS8/uo15BN0Fx7dOpiGrR3fX3MM31QW3bgzcgRtNDmC0mddS5t2tQLt3V8Z0PSSUgdk4jz+klKUAFxk7NytljYk2w2VYzq14ul1PGN9uQrhR7nqMZNUBdHYvAG1AMOhNZn3cePx/SKP2B720EoKkvw==
DKIM-Signature: v=1; a=rsa-sha256; c=simple; d=taugh.com; h=date:message-id:from:to:cc:subject:in-reply-to:mime-version:content-type:content-transfer-encoding:cleverness; s=12240.60651420.k2103; bh=zYEQXqyQCTPpxPQOEG+9kkcOxoLAyo1LpWPkilPw6e4=; b=vxDceQyGGaS4YAa31+haRYw3xAxipb6jeUNYIvRvInFguzSrziUDNR4JmElucmWQwKFry+SLfpmwEdpVj38Amdh1T9cGUmjpFMAt5nNVJglQZFMdDYcNO7FEcafXRHkKkhevLylMIse3WKoL9+WiR6pJIdqoGYhTPNwGx9oLl/7EL3Bb2K6y3Q9dvjXVKEikxtrdwhU+SflFvoviurcSwlcVJfvAhAM0r2Wj3CuOSqA8Ig1ln1ea4PJKlXlalLR7cDR1uUAmZ2VOHPKNbquYw9IRKMVVhJJSq7vxBkfPM/eewo86YUNQDBteOjjoW/mxuN8KbEoZWEe2z6E7qDvTSA==
Received: from ary.qy ([IPv6:2001:470:1f07:1126::78:696d:6170]) by imap.iecc.com ([IPv6:2001:470:1f07:1126::78:696d:6170]) with ESMTPS (TLS1.2 ECDHE-RSA AES-256-GCM AEAD) via TCP6; 01 Apr 2021 00:30:23 -0000
Received: by ary.qy (Postfix, from userid 501) id 713A871BE253; Wed, 31 Mar 2021 20:30:22 -0400 (EDT)
Date: Wed, 31 Mar 2021 20:30:22 -0400
Message-Id: <20210401003023.713A871BE253@ary.qy>
From: John Levine <johnl@taugh.com>
To: ietf-smtp@ietf.org
Cc: marka@isc.org
In-Reply-To: <992B07C8-5689-4092-A9CC-446731F5A114@isc.org>
Organization: Taughannock Networks
X-Headerized: yes
Cleverness: minimal
Mime-Version: 1.0
Content-type: text/plain; charset="utf-8"
Content-transfer-encoding: 8bit
Archived-At: <https://mailarchive.ietf.org/arch/msg/ietf-smtp/nnfrL8zWqgDrcDyqT2gjPSV4Vj8>
Subject: Re: [ietf-smtp] MTS-STS validation when MX host points to a CNAME, violating RFC 2181 § 10.3
X-BeenThere: ietf-smtp@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Discussion of issues related to Simple Mail Transfer Protocol \(SMTP\) \[RFC 821, RFC 2821, RFC 5321\]" <ietf-smtp.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ietf-smtp>, <mailto:ietf-smtp-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ietf-smtp/>
List-Post: <mailto:ietf-smtp@ietf.org>
List-Help: <mailto:ietf-smtp-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ietf-smtp>, <mailto:ietf-smtp-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 01 Apr 2021 00:30:33 -0000

It appears that Mark Andrews  <marka@isc.org> said:
>You need properly read the quoted section that talks about MX target being a CNAME.
>In particular this sentence from RFC 5321, section 5.1:
>
>   Any other response, specifically including a value that will return a
>   CNAME record when queried, lies outside the scope of this Standard.
>
>In other words “It is your problem if the target of the MX refers to a CNAME
>and things break."
>
>The MX records for n0.lt are NOT RFC compliant.  The target points to a CNAME.

Quite right.

"Doctor, doctor, it hurts when I do this."

"So don't do that."

R's,
John

v2.23.0 | Report a Bug | By Email