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Vulnerability record · CVE-2023-51764 · published 24 December 2023

CVE-2023-51764: Postfix insufficient verification of data authenticity vulnerability

Postfix · Postfix

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.

5.3 CVSS 3.1 Medium EPSS 2.6% · top 15.0% CWE-345 · Insufficient verification of data authenticity
5.3CVSS 3.1 base score
2.6%EPSS exploitation probability, 30 days
NoNot in CISA KEV
3Affected product versions listed by NVD
36References, 8 tagged exploit
17 Jun 2026Last modified by NVD

Description

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

Affected products

3 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://www.openwall.com/lists/oss-security/2023/12/24/1 Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2023/12/25/1 Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2024/05/09/3
https://access.redhat.com/security/cve/CVE-2023-51764 Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2255563 Issue TrackingThird Party Advisory
https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html Technical Description
https://github.com/duy-31/CVE-2023-51764 ExploitThird Party Advisory
https://github.com/eeenvik1/CVE-2023-51764 ExploitThird Party Advisory
https://lists.debian.org/debian-lts-announce/2024/01/msg00020.html
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JQ5WXFCW2N6G2PH3JXDTYW5
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QRLF5SOS7TP5N7FQSEK2NFN
https://lwn.net/Articles/956533/
https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/ Technical DescriptionThird Party Advisory
https://www.openwall.com/lists/oss-security/2024/01/22/1
https://www.postfix.org/announcements/postfix-3.8.5.html
https://www.postfix.org/smtp-smuggling.html ExploitMitigationVendor Advisory
https://www.youtube.com/watch?v=V8KPV96g1To Exploit
http://www.openwall.com/lists/oss-security/2023/12/24/1 Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2023/12/25/1 Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2024/05/09/3
https://access.redhat.com/security/cve/CVE-2023-51764 Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2255563 Issue TrackingThird Party Advisory
https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html Technical Description
https://github.com/duy-31/CVE-2023-51764 ExploitThird Party Advisory
https://github.com/eeenvik1/CVE-2023-51764 ExploitThird Party Advisory
https://lists.debian.org/debian-lts-announce/2024/01/msg00020.html
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JQ5WXFCW2N6G2PH3JXDTYW5
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QRLF5SOS7TP5N7FQSEK2NFN
https://lists.fedoraproject.org/archives/list/[email protected]/message/JQ5WXFCW2N6G2PH3JXDTYW5PH
https://lists.fedoraproject.org/archives/list/[email protected]/message/QRLF5SOS7TP5N7FQSEK2NFNB4
https://lwn.net/Articles/956533/
https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/ Technical DescriptionThird Party Advisory
https://www.openwall.com/lists/oss-security/2024/01/22/1
https://www.postfix.org/announcements/postfix-3.8.5.html
https://www.postfix.org/smtp-smuggling.html ExploitMitigationVendor Advisory
https://www.youtube.com/watch?v=V8KPV96g1To Exploit

Track CVE-2023-51764 inside VULONE

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Source: NIST National Vulnerability Database (record CVE-2023-51764), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.