Re: [dmarc-ietf] Tickets 98 and 99 -- fake reports are not a problem and if they were authentication would not help

Michael Thomas <mike@mtcc.com> Mon, 25 January 2021 15:18 UTC

Return-Path: <mike@fresheez.com>
X-Original-To: dmarc@ietfa.amsl.com
Delivered-To: dmarc@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id E8C6F3A1474 for <dmarc@ietfa.amsl.com>; Mon, 25 Jan 2021 07:18:00 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: 0.151
X-Spam-Level:
X-Spam-Status: No, score=0.151 tagged_above=-999 required=5 tests=[DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HEADER_FROM_DIFFERENT_DOMAINS=0.249, HTML_MESSAGE=0.001, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=no autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=mtcc.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 g6ePK_ZtU6k7 for <dmarc@ietfa.amsl.com>; Mon, 25 Jan 2021 07:17:59 -0800 (PST)
Received: from mail-pg1-x535.google.com (mail-pg1-x535.google.com [IPv6:2607:f8b0:4864:20::535]) (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 837473A146E for <dmarc@ietf.org>; Mon, 25 Jan 2021 07:17:59 -0800 (PST)
Received: by mail-pg1-x535.google.com with SMTP id t25so1160076pga.2 for <dmarc@ietf.org>; Mon, 25 Jan 2021 07:17:59 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mtcc.com; s=fluffulence; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-language; bh=Xq/56F7cgAQd9hIgU/jVf7p5hHdUJLss9scp6TJ0HZk=; b=ByBHNMmmqGfGrHA18+f8dDkG4/4sI1qoysJOfIpw3XxqkV7A3zuOBGvyFkCXj8yipY bSW3yyjx4SRiLO7BRm8hRwUZKCQzv5cC+p5/puJKtJ3Nprl0+LCQszPDYqSyE+aRWeBy STjsSVQdt4MNNx807L437o1jjSbdTfPyQueeZFH/z2tmBRgZAy/K4sJOS3rJkKOEBu5p 6vm63udDAlQT2206bUhfw12CjuDsThFVMPp3HtlDcmaQGipH3DtT3wGmG6ZvjrM2umTB vH8Q2dahQf0izGPR5tNQjD0/TWux+KtDpK3SZL0CT6qWKU7FhpvlHsz7iurACm4x9zWO 5zhA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language; bh=Xq/56F7cgAQd9hIgU/jVf7p5hHdUJLss9scp6TJ0HZk=; b=aF2cruJXyXmZMMskWS3bzrHUtcTIlT3B02k2QVDeUvR3+EbS+3Ac5fVPriPcvwL/Qw fuTskVtNNdzYrNidPjUq02zKm4I/gVfpKG2CDcoABEO0B+Y+IcDkQMgp0z6atQgXtWgr V/ex0l4JsZZyd0RiSorLJlYPM+YfANrn2JboY5UakeYRwMbJsEBY3YX9c63TqrCImqR5 omfSP0Y5v/l7p+P9vbSfTNjwrO6gL0CUub1vX8m9ClZlTblXEEmSHAzIl5UpbrzXPEnc btcB8wWiLsnsUSnGGgGRa3QUzbvZkuDh6wv8ENiih2X1q+12WgDw6s3/iT73gerFWDgC XB8w==
X-Gm-Message-State: AOAM533eKuIzXQTBEtpwLv/+B2Ie8n7hZxu0NVIpVUDBIFkdOkVoXl8Z /GpoRbJJhL2QJW0yhYEkpsJ/nV/hxFSLjA==
X-Google-Smtp-Source: ABdhPJwp+zYC7BDkO7YBqcjAFs2gZ+TOnc5uCm70MWFVVCrYyswLtNnsPNyKXGDi4IxiUu6uNPVlHw==
X-Received: by 2002:a62:a508:0:b029:1ba:621:ff29 with SMTP id v8-20020a62a5080000b02901ba0621ff29mr918997pfm.44.1611587878497; Mon, 25 Jan 2021 07:17:58 -0800 (PST)
Received: from mike-mac.lan (107-182-35-22.volcanocom.com. [107.182.35.22]) by smtp.gmail.com with ESMTPSA id hs21sm18953170pjb.6.2021.01.25.07.17.57 for <dmarc@ietf.org> (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 25 Jan 2021 07:17:57 -0800 (PST)
To: dmarc@ietf.org
References: <34317129-8225-fb38-4ad3-e1b9ffed21fb@iecc.com> <9c84fa50-d23c-a794-fc62-09788ac383a9@mtcc.com> <CAHej_8mTaFo7aESFk4pHjbqbheriYPoAy6f+HhcE6ASVJSyViA@mail.gmail.com>
From: Michael Thomas <mike@mtcc.com>
Message-ID: <df867378-5da0-b912-2a0f-b2081d1f2437@mtcc.com>
Date: Mon, 25 Jan 2021 07:17:56 -0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.0
MIME-Version: 1.0
In-Reply-To: <CAHej_8mTaFo7aESFk4pHjbqbheriYPoAy6f+HhcE6ASVJSyViA@mail.gmail.com>
Content-Type: multipart/alternative; boundary="------------A56748F1AAF581010D9F620E"
Content-Language: en-US
Archived-At: <https://mailarchive.ietf.org/arch/msg/dmarc/H13Gxh7PTIt_YqR1WGOeBOsWkjs>
Subject: Re: [dmarc-ietf] Tickets 98 and 99 -- fake reports are not a problem and if they were authentication would not help
X-BeenThere: dmarc@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Domain-based Message Authentication, Reporting, and Compliance \(DMARC\)" <dmarc.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/dmarc>, <mailto:dmarc-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/dmarc/>
List-Post: <mailto:dmarc@ietf.org>
List-Help: <mailto:dmarc-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/dmarc>, <mailto:dmarc-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 25 Jan 2021 15:18:01 -0000

On 1/25/21 5:25 AM, Todd Herr wrote:
> On Sun, Jan 24, 2021 at 9:53 PM Michael Thomas <mike@mtcc.com 
> <mailto:mike@mtcc.com>> wrote:
>
>
>     On 1/24/21 6:29 PM, John R. Levine wrote:
>     > I realized why the arguments about whether to require
>     authentication
>     > on reports are pointless.
>     >
>     A blatant assertion. The onus of proof is with people who say we
>     should
>     accept information from unknown sources. Extraordinary claims require
>     extraordinary evidence. I have been doing security related stuff for
>     long enough to know that being humble in the face of adversaries
>     is the
>     most prudent course. State actors can get involved when they
>     figure they
>     can game things to their advantage. To be dismissive is complete
>     hubris.
>
>
> I've spent several days thinking about these tickets, and for the life 
> of me I can't see what the payoff might be for someone to forge a 
> DMARC report.
>
> I suppose nominally there's a denial of service risk, where a bad 
> actor could flood a rua or ruf mailbox with forged reports or just 
> email in general, but that's going to exist whether or not the 
> "reports" are DKIM-signed.

The main thing I've learned over the years of dealing with security is 
to not underestimate what a motivated attacker can do. Your imagination 
is not the same as their imagination. Closing #98 in particular is 
absolutely ridiculous: the report should already have a DKIM signature 
or SPF so it's just a matter of making sure its valid. Why would you 
*not* want to insure that? The amount of justification for *not* having 
the receiver authenticate it is a mountain. The amount of effort to 
authenticate it is trivial for mail. Levine's dismissal of security 
concerns because he has anecdotal "evidence" from a backwater domain 
carries no weight at all.

Mike