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Date: Tue, 17 Sep 2019 18:54:53 +0200
From: Salvatore Bonaccorso <>
Subject: Re: OpenDMARC signature bypass with multiple From


On Wed, Sep 11, 2019 at 12:43:19PM +0200, Hanno Böck wrote:
> Hi,
> Protonmail reported about a phishing incident in July:
> This had this somewhat mysterious chapter:
> "Furthermore, the attackers attempted to exploit an unpatched
> vulnerability in an open source software that is widely used by email
> providers in an effort to bypass spam and abuse filters. We were
> previously aware of this vulnerability and have already been watching
> it for some time, but we will not disclose it here because the software
> in question is not developed by ProtonMail, and it has not yet been
> patched by the software maintainers. This vulnerability, however, is
> not widely known and indicates a higher level of sophistication on the
> part of the attackers."
> After asking protonmail multiple times for a statement they answered
> and I learned that it's about this issue in OpenDMARC:
> It's an issue where by specifying multiple From addresses only one of
> them gets DMARC-checked.
> There's no reaction from the OpenDMARC developers and it's unclear
> whether it's still actively developed. Given this is already actively
> exploited I think people should be aware of it and distros should
> probably apply the patch from the PR.

MITRE has assigned CVE-2019-16378 for this issue (requested via the


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