Re: [dmarc-ietf] Forensic report loops are a problem

Alessandro Vesely <vesely@tana.it> Thu, 28 January 2021 12:41 UTC

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From: Alessandro Vesely <vesely@tana.it>
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Subject: Re: [dmarc-ietf] Forensic report loops are a problem
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On Thu 28/Jan/2021 04:17:06 +0100 Steven M Jones wrote:
> On 1/27/21 12:47, Murray S. Kucherawy wrote:
>> On Wed, Jan 27, 2021 at 12:37 PM John Levine wrote:
>>
>>> I still don't understand why failure reports about messages that happen
>>> to be failure reports are in any way special. >>
>> Loop detection in RFC 5321 is a normative MUST because of the obvious 
>> operational problems it creates.  Maybe I'm being thick, but right now I
>> don't see how this is different, apart from the fact that each message is
>> distinct; you're still causing a problem by turning this on without a care
>> in the world about whether two verifiers start spamming each other. >
> There's coverage in 7489 Section 7.2 that a domain owner can inadvertently
> DDoS themselves via failure reports. And that still surprised many
> implementers, even though it seemed obvious to them in retrospect. >
> This case is even less obvious, and we still have questions coming in about
> it from new implementers. >
> I don't think it's a security consideration because it doesn't scale up
> the way "ruf" can, so it deserves a brief mention here. But I would
> rephrase Ale's last sentence:
> 
> 
> 3.3.  Transport
> 
>     Email streams carrying DMARC failure reports MUST conform to the
>     DMARC mechanism, thereby resulting in an aligned "pass".  Special
>     care must be taken for authentication, as failure to authenticate
>     failure reports may result in mail loops.  These loops can be mitigated
>     by sending reports from a domain or subdomain that doesn't request
>     reports, or by performing rate limiting for report receiving mailboxes.


I rephrased it further:

3.3.  Transport

    Email streams carrying DMARC failure reports MUST conform to the
    DMARC mechanism, thereby resulting in an aligned "pass".  Special
    care must be taken of authentication, as failure to authenticate
    failure reports may result in mail loops.  These loops can be
    mitigated by sending reports from a domain or subdomain that doesn't
    request reports, or by performing rate limiting especially for
    failures related to messages received at addresses published in a
    ruf= tag.


Best
Ale
--