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.
Fix
Public exploits 4
- Double-q1015/CVE-2023-51764 PoC on GitHub
- d4op/CVE-2023-51764-POC PoC on GitHub
- duy-31/CVE-2023-51764 PoC on GitHub
- eeenvik1/CVE-2023-51764 PoC on GitHub
Each line links to the index that lists it, never to exploit code. Exploit-DB's "verified" and a Metasploit rank of good or better count as verified; a PoC-in-GitHub entry is a repository's claim.
Patch, vendor advisory and mitigation references on NVD 2
- https://www.postfix.org/smtp-smuggling.html Exploit, Mitigation, Vendor Advisory
- https://www.postfix.org/smtp-smuggling.html Exploit, Mitigation, Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 5.3 · postfix, fedoraproject, redhatNVD modified 2026-10-08 21:17
Affected (CPE criteria) 5
cpe:2.3:a:postfix:postfix:*:*:*:*:*:*:*:*cpe:2.3:o:fedoraproject:fedora:38:*:*:*:*:*:*:*cpe:2.3:o:fedoraproject:fedora:39:*:*:*:*:*:*:*cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:*
References 36
- http://www.openwall.com/lists/oss-security/2023/12/24/1 Mailing List, Third Party Advisory
- http://www.openwall.com/lists/oss-security/2023/12/25/1 Mailing List, Third 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 Tracking, Third Party Advisory
- https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html Technical Description
- https://github.com/duy-31/CVE-2023-51764 Exploit, Third Party Advisory
- https://github.com/eeenvik1/CVE-2023-51764 Exploit, Third 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/JQ5WXFCW2N6G2PH3JXDTYW5PH5EBQEGO/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QRLF5SOS7TP5N7FQSEK2NFNB44ISVTZC/
- https://lwn.net/Articles/956533/
- https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/ Technical Description, Third 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 Exploit, Mitigation, Vendor Advisory
- https://www.youtube.com/watch?v=V8KPV96g1To Exploit
- http://www.openwall.com/lists/oss-security/2023/12/24/1 Mailing List, Third Party Advisory
- http://www.openwall.com/lists/oss-security/2023/12/25/1 Mailing List, Third 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 Tracking, Third Party Advisory
- https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html Technical Description
- https://github.com/duy-31/CVE-2023-51764 Exploit, Third Party Advisory
- https://github.com/eeenvik1/CVE-2023-51764 Exploit, Third 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/JQ5WXFCW2N6G2PH3JXDTYW5PH5EBQEGO/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QRLF5SOS7TP5N7FQSEK2NFNB44ISVTZC/
- https://lists.fedoraproject.org/archives/list/[email protected]/message/JQ5WXFCW2N6G2PH3JXDTYW5PH5EBQEGO/
- https://lists.fedoraproject.org/archives/list/[email protected]/message/QRLF5SOS7TP5N7FQSEK2NFNB44ISVTZC/
- https://lwn.net/Articles/956533/
- https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/ Technical Description, Third 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 Exploit, Mitigation, Vendor Advisory
- https://www.youtube.com/watch?v=V8KPV96g1To Exploit