CVE-2023-51764 — Postfix through 3

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 in

01What is this vulnerability?

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…

02Affected products

No structured affected-product list available — see references below for vendor advisories.

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Ask SARA in chat to draft a starting detection for this CVE in your stack of choice.

07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2023-12-24T05:15:08.273
• Last modified: 2026-10-08T21:17:49.743

09References

• www.openwall.com — http://www.openwall.com/lists/oss-security/2023/12/24/1
• www.openwall.com — http://www.openwall.com/lists/oss-security/2023/12/25/1
• www.openwall.com — http://www.openwall.com/lists/oss-security/2024/05/09/3
• access.redhat.com — https://access.redhat.com/security/cve/CVE-2023-51764
• bugzilla.redhat.com — https://bugzilla.redhat.com/show_bug.cgi?id=2255563
• fahrplan.events.ccc.de — https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html
• github.com — https://github.com/duy-31/CVE-2023-51764
• github.com — https://github.com/eeenvik1/CVE-2023-51764
• lists.debian.org — https://lists.debian.org/debian-lts-announce/2024/01/msg00020.html
• lists.fedoraproject.org — https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedorapro…