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Debian LTS Advisory DLA-3725-1                debian-lts@lists.debian.org
https://www.debian.org/lts/security/                   Bastien Roucariès
January 30, 2024                              https://wiki.debian.org/LTS
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Package        : postfix
Version        : 3.4.23-0+deb10u2
CVE ID         : CVE-2023-51764
Debian Bug     : 1059230

Postfix, a popular mail server, 
allowed SMTP smuggling unless configured with
smtpd_data_restrictions=reject_unauth_pipelining
and smtpd_discard_ehlo_keywords=chunking
(or certain other options that exist in recent versions).

Remote attackers can use a published exploitation technique to
inject e-mail messages with a spoofed MAIL FROM address,
allowing bypass of an SPF protection mechanism.

This occurs because Postfix supported . but
some other popular e-mail servers do not.

To prevent attack variants (by always disallowing  without ),
a different solution is required, such as setting the backported
configuration option smtpd_forbid_bare_newline=yes

For Debian 10 buster, this problem has been fixed in version
3.4.23-0+deb10u2.

We recommend that you upgrade your postfix packages.

For the detailed security status of postfix please refer to
its security tracker page at:
https://security-tracker.debian.org/tracker/source-package/postfix

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://wiki.debian.org/LTS