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Date: Sat, 23 Dec 2023 00:40:06 +0800
From: "Alexander E. Patrakov" <>
Subject: Re: Re: New SMTP smuggling attack

On Fri, Dec 22, 2023 at 11:57 PM Rodrigo Freire <> wrote:
> On Fri, Dec 22, 2023 at 12:10 PM Erik Auerswald
> <> wrote:
> >   * The CERT/CC and VINCE involvement resulted in "there is no
> >     vulnerability".
> I'm trying to make sense of it - where's the compromise of the
> Confidentiality, Integrity or Availability of the affected mail
> servers?

The integrity of the sender's identity, as a minimum, is compromised
here. Normally, when relaying mail, servers add a "Received:" header
that specifies where they received the connection from. This allows
tracking down the true origin of the message. The smuggled message
does not have such a header and thus misrepresents the vulnerable
relay as the ultimate sender. Additionally, if the relay has
destination-based deny lists that deny some but not all addresses on
the destination domain, they are sidestepped.

Alexander E. Patrakov

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