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Date: Thu, 21 Dec 2023 15:36:33 +0100
From: Marcus Meissner <>
To: OSS Security List <>
Subject: New SMTP smuggling attack


As if we did not have sufficient protocol vulnerability work short before
Christmas break this year, here is one more:

While it looks like "old stuff", this is new quality.

tldr: The end of "SMTP data phase" with "<CR><LF>.<CR><LF>" is not
consistently implemented everywhere (e.g. when leaving out <CR> or
inserting \0 or so) and could lead to one server passing it through and
the other processing it, leading to mail spoofing.

The security report it for some custom email servers, but at least
Postfix announced mitigation work already:

Ciao, Marcus

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