--- id: CVE-2023-51764 title: >- 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) summary: >- 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 u… severity: medium cvss: 5.3 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N' cwe: - CWE-345 vendor: postfix product: postfix affected: - postfix < 3.5.23 - 'postfix >= 3.6.0, < 3.6.13' - 'postfix >= 3.7.0, < 3.7.9' - 'postfix >= 3.8.0, < 3.8.4' - fedora = 38 - fedora = 39 - enterprise_linux = 8.0 - enterprise_linux = 9.0 patched: - postfix 3.8.4 published: '2023-12-24' updated: '2026-10-08' sourceUpdated: '2026-10-08T21:17:49.743' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2023-51764' references: - url: 'http://www.openwall.com/lists/oss-security/2023/12/24/1' label: cve@mitre.org - url: 'http://www.openwall.com/lists/oss-security/2023/12/25/1' label: cve@mitre.org - url: 'http://www.openwall.com/lists/oss-security/2024/05/09/3' label: cve@mitre.org - url: 'https://access.redhat.com/security/cve/CVE-2023-51764' label: cve@mitre.org - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2255563' label: cve@mitre.org - url: 'https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html' label: cve@mitre.org - url: 'https://github.com/duy-31/CVE-2023-51764' label: cve@mitre.org - url: 'https://github.com/eeenvik1/CVE-2023-51764' label: cve@mitre.org - url: 'https://lists.debian.org/debian-lts-announce/2024/01/msg00020.html' label: cve@mitre.org - url: >- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JQ5WXFCW2N6G2PH3JXDTYW5PH5EBQEGO/ label: cve@mitre.org - url: >- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QRLF5SOS7TP5N7FQSEK2NFNB44ISVTZC/ label: cve@mitre.org - url: 'https://lwn.net/Articles/956533/' label: cve@mitre.org - url: >- https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/ label: cve@mitre.org - url: 'https://www.openwall.com/lists/oss-security/2024/01/22/1' label: cve@mitre.org - url: 'https://www.postfix.org/announcements/postfix-3.8.5.html' label: cve@mitre.org - url: 'https://www.postfix.org/smtp-smuggling.html' label: cve@mitre.org - url: 'https://www.youtube.com/watch?v=V8KPV96g1To' label: cve@mitre.org - url: 'http://www.openwall.com/lists/oss-security/2023/12/24/1' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'http://www.openwall.com/lists/oss-security/2023/12/25/1' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'http://www.openwall.com/lists/oss-security/2024/05/09/3' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://access.redhat.com/security/cve/CVE-2023-51764' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2255563' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://github.com/duy-31/CVE-2023-51764' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://github.com/eeenvik1/CVE-2023-51764' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://lists.debian.org/debian-lts-announce/2024/01/msg00020.html' label: af854a3a-2127-422b-91ae-364da2661108 - url: >- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/JQ5WXFCW2N6G2PH3JXDTYW5PH5EBQEGO/ label: af854a3a-2127-422b-91ae-364da2661108 - url: >- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QRLF5SOS7TP5N7FQSEK2NFNB44ISVTZC/ label: af854a3a-2127-422b-91ae-364da2661108 - url: >- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/JQ5WXFCW2N6G2PH3JXDTYW5PH5EBQEGO/ label: af854a3a-2127-422b-91ae-364da2661108 - url: >- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QRLF5SOS7TP5N7FQSEK2NFNB44ISVTZC/ label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://lwn.net/Articles/956533/' label: af854a3a-2127-422b-91ae-364da2661108 - url: >- https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/ label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://www.openwall.com/lists/oss-security/2024/01/22/1' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://www.postfix.org/announcements/postfix-3.8.5.html' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://www.postfix.org/smtp-smuggling.html' label: af854a3a-2127-422b-91ae-364da2661108 - url: 'https://www.youtube.com/watch?v=V8KPV96g1To' label: af854a3a-2127-422b-91ae-364da2661108 tags: - nvd - exploit-available epss: 0.02635 epssPercentile: 0.85102 exploits: github: 4 githubRepos: - 'https://github.com/duy-31/CVE-2023-51764' - 'https://github.com/eeenvik1/CVE-2023-51764' - 'https://github.com/d4op/CVE-2023-51764-POC' checkedAt: '2026-10-09T10:30:36.514Z' exploitAvailable: true ingestedAt: '2026-10-08T22:11:53.760Z' --- ## Overview 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 . but some other popular e-mail servers do not. To prevent attack variants (by always disallowing without ), 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 - `postfix < 3.5.23` - `postfix >= 3.6.0, < 3.6.13` - `postfix >= 3.7.0, < 3.7.9` - `postfix >= 3.8.0, < 3.8.4` - `fedora = 38` - `fedora = 39` - `enterprise_linux = 8.0` - `enterprise_linux = 9.0` ## Remediation Upgrade past the affected range: - `postfix 3.8.4`