On 17/11/22 04:59, Alessandro Vesely wrote:
> In the context of a replay attack, the important cases are:
>
> 1. the MLM does not break the original DKIM signature
> 2. the MLM applies its own ARC/DKIM signature which is itself used in a reply
> attack
I fancied an experiment where a MLM offers a per-subscriber choice on whether
to munge From: or not. The way I envisaged it was to have users whitelist the
ARC/ DKIM signing domain concurrently with their opting for non-munged From:.
Mailbox providers could maintain per-user whitelists. But it was rejected by
the ISE...
That's a lot of moving parts. Quite apart from needing mailbox providers
needing to provide a means to do this, it requires that the user making
the munging decision act in concert with all of the other list
subscribers (if I specify non-munging then all other subscribers must
whitelist in order to receive my posts), which doesn't seem at all feasible.
>> which smaller mailbox providers cannot use?
>
> Smaller mailbox providers operating without the benefit of security data of
> some sort, yes.
What security data?
Whatever a data provider might provide that's helpful. Most server-side
anti-spam products already include some sort of data exchange (or at
least feed) to allow decision-making by small receivers to be supported
by a much broader picture of the behaviour of abusers than they can
obtain from their own logs.
- Roland
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