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.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | postfix | 3.8.4-1 | — |
| Debian 13 | postfix | 3.8.4-1 | — |
| Debian 12 | postfix | 3.7.9-0+deb12u1 | — |
| Debian 10 | postfix | 3.4.23-0+deb10u2 | DLA-3725-1 |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 22.04 LTS | postfix | 3.6.4-1ubuntu1.3 | USN-6591-2, USN-6591-1 |
| Ubuntu 20.04 LTS | postfix | 3.4.13-0ubuntu1.4 | USN-6591-2, USN-6591-1 |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 18.04 LTS | postfix | 3.3.0-1ubuntu0.4+esm3 | USN-6591-2, USN-6591-1 |
| Ubuntu Pro 16.04 LTS | postfix | 3.1.0-3ubuntu0.4+esm3 | USN-6591-2, USN-6591-1 |
| Ubuntu Pro 14.04 LTS | postfix | 2.11.0-1ubuntu1.2+esm3 | USN-6591-2, USN-6591-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 9 | postfix +8 | 2:3.5.25-1.el9 | RHSA-2024:9243 |
AlmaLinux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux 9 | postfix +8 | 2:3.5.25-1.el9 | ALSA-2024:9243 |
Rocky Linux
Errata ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Rocky Linux 9 | postfix | 2:3.5.25-1.el9 | RLSA-2024:9243 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP5 | postfix +1 | 3.7.3-150500.3.11.1 | SUSE-SU-2023:4981-1 |
| SLES 15 SP4 | postfix +1 | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
| SLES 15 SP3 | postfix +1 | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
| SLES 12 SP5 | postfix | 3.2.10-3.30.1 | SUSE-SU-2024:1149-1 |
Show 9 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 15 SP4 | postfix +1 | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
| SLES for SAP 15 SP3 | postfix +1 | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
| SLES for SAP 12 SP5 | postfix | 3.2.10-3.30.1 | SUSE-SU-2024:1149-1 |
| SLE Real Time 15 SP4 | postfix | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
| SLE HPC 15 SP4 | postfix +1 | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
| SLE HPC 15 SP3 | postfix +1 | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
| SUSE Manager Server 4.3 | postfix | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
| SUSE Manager Proxy 4.3 | postfix | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
| SUSE Enterprise Storage 7.1 | postfix +1 | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | postfix | 3.8.4-2.1 | openSUSE-SU-2024:13538-1 |
| openSUSE Leap 15.5 | postfix +1 | 3.7.3-150500.3.11.1 | SUSE-SU-2023:4981-1 |
| openSUSE Leap 15.4 | postfix +1 | 3.5.9-150300.5.15.1 | SUSE-SU-2024:0012-1 |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | postfix +8 | 2:3.7.2-4.amzn2023.0.5 | ALAS2023-2024-495 |
| Amazon Linux 2 | postfix +2 | 2:2.10.1-6.amzn2.0.4 | ALAS2-2024-2420 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | postfix | 3.9.0-1 | — |
| Azure Linux 2 (CBL-Mariner) | postfix | 3.7.0-3 | — |
Oracle Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Oracle Linux 9 | postfix +8 | 2:3.5.25-1.el9 | ELSA-2024-9243 |
Public exploits
Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.
Third-party code, not reviewed by us. Public PoCs are sometimes fake or contain malware. Read the code first and run it only in an isolated lab, against systems you are authorised to test.
GitHub 4 repositories
-
duy-31/CVE-2023-51764 ★ 23 · Dec 26, 2023
Postfix SMTP Smuggling - Expect Script POC
-
eeenvik1/CVE-2023-51764 ★ 4 · Dec 28, 2023
PoC CVE-2023-51764
-
d4op/CVE-2023-51764-POC ★ 1 · Dec 31, 2023
just idea, no cp pls
-
Double-q1015/CVE-2023-51764 ★ 0 · Jan 5, 2024
CVE-2023-51764 poc
Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.
Advisories 15
- WID-SEC-2026-3076 Dovecot: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 12, 2026
- ALSA-2024:9243 Moderate: postfix security update AlmaLinux Security Advisories · Oct 29, 2026
- USN-6591-1 postfix vulnerability Ubuntu Security Notices (USN) · Jun 29, 2026
- USN-6591-2 postfix update Ubuntu Security Notices (USN) · Jun 29, 2026
- RHSA-2024:9243 Red Hat Security Advisory: postfix security update Red Hat Security Advisories (RHSA) · Jun 26, 2026
- DLA-3725-1 postfix - security update Debian Security (DSA / DLA) · Mar 9, 2026
- SUSE-SU-2023:4981-1 Security update for postfix SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2024:1149-1 Security update for postfix SUSE / openSUSE Security Updates · Feb 4, 2026
- SUSE-SU-2024:0012-1 Security update for postfix SUSE / openSUSE Security Updates · Feb 4, 2026
- openSUSE-SU-2024:13538-1 postfix-3.8.4-2.1 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
- RLSA-2024:9243 Moderate: postfix security update Rocky Linux Security Advisories · Oct 9, 2025
- ELSA-2024-9243 Moderate: postfix security update (Oracle Linux 9) Oracle Linux Security Advisories (ELSA) · Nov 14, 2024
- WID-SEC-2023-3206 SMTP Implementierungen: Schwachstelle ermöglicht Umgehen von Sicherheitsvorkehrungen BSI CERT-Bund (WID) · Nov 11, 2024
- ALAS2023-2024-495 Important: postfix security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Jan 22, 2024
- ALAS2-2024-2420 Important: postfix security update (Amazon Linux 2) Amazon Linux Security Center (ALAS) · Jan 22, 2024
References
- https://www.postfix.org/smtp-smuggling.html
- https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/
- [oss-security] 20231224 Re: Re: New SMTP smuggling attack mailing-list
- [oss-security] 20231225 Re: Re: New SMTP smuggling attack mailing-list
- https://bugzilla.redhat.com/show_bug.cgi?id=2255563
- https://access.redhat.com/security/cve/CVE-2023-51764
- https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html
- https://github.com/eeenvik1/CVE-2023-51764
- https://github.com/duy-31/CVE-2023-51764
- https://www.youtube.com/watch?v=V8KPV96g1To
- FEDORA-2024-c839e7294f vendor-advisory
- FEDORA-2024-5c186175f2 vendor-advisory
- https://lwn.net/Articles/956533/
- https://www.openwall.com/lists/oss-security/2024/01/22/1
- https://www.postfix.org/announcements/postfix-3.8.5.html
- [debian-lts-announce] 20240130 [SECURITY] [DLA 3725-1] postfix security update mailing-list
- [oss-security] 20240508 Re: New SMTP smuggling attack mailing-list