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.

CVSS 3.1

5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS

2.6% chance of exploitation in the next 30 days; higher than 85% of CVEs (scores of 2026-10-25)

CWE

CWE-345

Published

2023-12-24

Modified

2026-10-08

Record from

the NVD, synced 2026-10-19

Affected

• fedoraproject:fedora
• postfix:postfix
• redhat:enterprise_linux

References

• http://www.openwall.com/lists/oss-security/2023/12/24/1
• http://www.openwall.com/lists/oss-security/2023/12/25/1
• http://www.openwall.com/lists/oss-security/2024/05/09/3
• https://access.redhat.com/security/cve/CVE-2023-51764
• https://bugzilla.redhat.com/show_bug.cgi?id=2255563

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