MEDIUM 5.3 Microsoft

CVE-2023-51764

Postfix through 3.8.5 allows 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 supports <LF>.<CR><LF> but some other popular e-mail servers do not. To prevent attack variants (by always disallowing <LF> without <CR>) a different solution is required such as the smtpd_forbid_bare_newline=yes option with a Postfix minimum version of 3.5.23 3.6.13 3.7.9 3.8.4 or 3.9.

Microsoft Security Update 2023-Dec: Postfix through 3.8.5 allows 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 supports <LF>.<CR><LF> but some other popular e-mail servers do not. To prevent attack variants (by always disallowing <LF> without <CR>) a different solution is required such as the smtpd_forbid_bare_newline=yes option with a Postfix minimum version of 3.5.23 3.6.13 3.7.9 3.8.4 or 3.9.

Affected Products

References

Published: 2023-12-12 · Source: Microsoft · Feed updated: 2026-09-03
This medium severity vulnerability with a CVSS score of 5.3 was published on 2023-12-12 via Microsoft. Affected: cbl2 postfix 3.7.4-1 on CBL Mariner 2.0, cbl2 postfix 3.7.0-3 on CBL Mariner 2.0, azl3 postfix 3.9.0-1 on Azure Linux 3.0 and 1 more.
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