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Re: [dmarc-ietf] Reversing modifications from mailing lists

John Levine <johnl@taugh.com> Wed, 01 December 2021 19:10 UTC

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From: John Levine <johnl@taugh.com>
To: dmarc@ietf.org
Cc: vesely@tana.it
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Subject: Re: [dmarc-ietf] Reversing modifications from mailing lists
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It appears that Alessandro Vesely  <vesely@tana.it> said:
>I'm not clear about the last but one paragraph of that section:
>
>    An example of such an attack includes altering the MIME structure,
>    exploiting lax HTML parsing in the MUA, and defeating duplicate
>    message detection algorithms.
>
>I'm going to file an errata about it.  Altering the MIME structure is only 
>possible if the value of l= is less than the original message length. 

I wish you hadn't.  I think the original concern was for sloppy MIME that
forgot the -- after the last part.

>Anyway, I wouldn't want to authenticate a message that underwent an HTML footer 
>addition, because it can completely replace the original content in the end 
>recipient's eyes.  My draft requires footers to be plain text.

Yet that's exactly what one of the largest discussion group services in the world did.
As I keep pointing out, this is like an UNCOL, it does not generalize enough to be useful.

On the other hand, ARC handles this just fine.

R's,
John

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