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

Michael Thomas <> Mon, 25 January 2021 15:18 UTC

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From: Michael Thomas <>
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Date: Mon, 25 Jan 2021 07:17:56 -0800
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Subject: Re: [dmarc-ietf] Tickets 98 and 99 -- fake reports are not a problem and if they were authentication would not help
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On 1/25/21 5:25 AM, Todd Herr wrote:
> On Sun, Jan 24, 2021 at 9:53 PM Michael Thomas < 
> <>> 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.