Re: [dmarc-ietf] Ticket #28 - Failure report mail loops

"Murray S. Kucherawy" <superuser@gmail.com> Mon, 07 December 2020 07:16 UTC

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From: "Murray S. Kucherawy" <superuser@gmail.com>
Date: Sun, 6 Dec 2020 23:15:57 -0800
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To: Alessandro Vesely <vesely@tana.it>
Cc: dmarc-ietf <dmarc@ietf.org>
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Subject: Re: [dmarc-ietf] Ticket #28 - Failure report mail loops
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On Fri, Dec 4, 2020 at 3:10 AM Alessandro Vesely <vesely@tana.it> wrote:

> We would like to close this ticket by Dec 18, two weeks from now, so
> please get
> on it.
>
> The ticket originated from John's comment, in May 2019:
>
>      Apropos recent discussions, we could recommend that failure reports be
>      rate limited per recipient both to break loops and to deter indirect
>      mail bombing.
>
>
> The current draft discusses the topic toward the end of the introduction
> of
> Section 3, before the first subsection:
>
>     An obvious consideration is the denial-of-service attack that can be
>     perpetrated by an attacker who sends numerous messages purporting to
>     be from the intended victim Domain Owner but that fail both SPF and
>     DKIM; this would cause participating Mail Receivers to send failure
>     reports to the Domain Owner or its delegate in potentially huge
>     volumes.  Accordingly, participating Mail Receivers are encouraged to
>     aggregate these reports as much as is practical, using the Incidents
>     field of the Abuse Reporting Format ([RFC5965]).  Various aggregation
>     techniques are possible, including the following:
>
>     *  only send a report to the first recipient of multi-recipient
>        messages;
>
>     *  store reports for a period of time before sending them, allowing
>        detection, collection, and reporting of like incidents;
>
>     *  apply rate limiting, such as a maximum number of reports per
>        minute that will be generated (and the remainder discarded).
>
>
> Some issues the WG may want to consider:
>
> 1.  That whole passage should be moved to its own subsection of Section 5,
> "Security Considerations".  Only a reference should be left in the intro.
>

Sure (though it's also fine where it is, IMHO).

2.  In the first *-bullet above, the sense of multi-recipient is
> ambiguous.  An
> explicit mention of ruf= might help.
>

I don't follow.

3.  The 2nd and 3rd *-bullets may need expansion.  Propose text in case.
>

Has anyone complained that they're too terse?

4.  Some explicit loop prevention specification may be added.  For example:
> 4.1.  send reports from a subdomain having a DMARC record without ruf=, or
> 4.2.  never send failure reports about failed reports.
>

The latter, which is consistent with SMTP never generating a bounce about a
bounce.

-MSK