Skip to content
Noroxi
NVD / CVE Program· CNA mitre

CVE-2023-51764: Postfix through 3.8.5 allows SMTP smuggling unless configured with smtpd_data_restrictions=reject_unauth_pipelining and…

Noroxi assessment

Priority: Monitor (action score 22/100)

  • Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
  • Probability of exploitation in the next 30 days: 2.6% (FIRST EPSS); higher than 85.6% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: postfix (AlmaLinux:9) 2:3.5.25-1.el9; postfix-cdb (AlmaLinux:9) 2:3.5.25-1.el9; postfix-ldap (AlmaLinux:9) 2:3.5.25-1.el9.

Low priority for now. Upgrade to postfix (AlmaLinux:9) 2:3.5.25-1.el9; postfix-cdb (AlmaLinux:9) 2:3.5.25-1.el9; postfix-ldap (AlmaLinux:9) 2:3.5.25-1.el9 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

MediumCVSS 5.3 · v3.1—Proof of concept Fix available
Published
Dec 24, 2023
Updated
Oct 8, 2026
EPSS
2.6% · 85th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
21 / 40 · 5.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
1 / 30 · 2.6%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • Proof of concept exists, no weaponized module
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2023-51764

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

One daily email digest (06:00 UTC); connect a webhook for KEV listings and weaponized exploits instantly.

Your free account also gets you

  • Stack alerts: add the products and versions you run, get the new CVEs that affect them
  • Uptime monitoring: 1 site, instant email when it goes down
  • Add your domain: subdomains and takeover risk scanned every week (1 domain)
  • 10 scans an hour on the security tools (3 a day without an account), an API key and MCP
  • All your scans in one panel: findings, what changed in the last scan, a report per domain or per client (PDF, share link)
All free tools

Sign up with email · Have an account? Sign in

Free account, no card. Unfollow any time.

Don't want an account? Get "Exploited this week" by email every MondayDon't want an account? RSS feed for postfix records
Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

We use this product, ask for help

Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
postfixpostfix
fedoraprojectfedora
redhatenterprise linux

Using postfix? Add it to your stack and be the first to know about CVEs like this one. (Email server)

Watch new CVEs for postfix

When you'll hear from us

  • when a new CVE affecting this product is published
  • when a record in your stack enters KEV or gets exploit code

One daily email digest (06:00 UTC); connect a webhook for KEV listings and weaponized exploits instantly.

Your free account also gets you

  • Stack alerts: add the products and versions you run, get the new CVEs that affect them
  • Uptime monitoring: 1 site, instant email when it goes down
  • Add your domain: subdomains and takeover risk scanned every week (1 domain)
  • 10 scans an hour on the security tools (3 a day without an account), an API key and MCP
  • All your scans in one panel: findings, what changed in the last scan, a report per domain or per client (PDF, share link)
All free tools

Sign up with email · Have an account? Sign in

Free account, no card. Unfollow any time.

Don't want an account? Get "Exploited this week" by email every Monday

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • fedoraproject fedora38
  • fedoraproject fedora39
  • postfix postfix3.7.0 and later · before 3.7.9
  • postfix postfix3.8.0 and later · before 3.8.4
  • postfix postfixbefore 3.5.23
  • postfix postfix3.6.0 and later · before 3.6.13
  • redhat enterprise linux8.0
  • redhat enterprise linux9.0

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:9postfixbefore 2:3.5.25-1.el92:3.5.25-1.el9
AlmaLinux:9postfix-cdbbefore 2:3.5.25-1.el92:3.5.25-1.el9
AlmaLinux:9postfix-ldapbefore 2:3.5.25-1.el92:3.5.25-1.el9
AlmaLinux:9postfix-lmdbbefore 2:3.5.25-1.el92:3.5.25-1.el9
AlmaLinux:9postfix-mysqlbefore 2:3.5.25-1.el92:3.5.25-1.el9
AlmaLinux:9postfix-pcrebefore 2:3.5.25-1.el92:3.5.25-1.el9
AlmaLinux:9postfix-perl-scriptsbefore 2:3.5.25-1.el92:3.5.25-1.el9
AlmaLinux:9postfix-pgsqlbefore 2:3.5.25-1.el92:3.5.25-1.el9
AlmaLinux:9postfix-sqlitebefore 2:3.5.25-1.el92:3.5.25-1.el9
Debian:10postfixbefore 3.4.23-0+deb10u23.4.23-0+deb10u2
Debian:12postfixbefore 3.7.9-0+deb12u13.7.9-0+deb12u1
Debian:13postfixbefore 3.8.4-13.8.4-1
openSUSE:Leap 15.4postfixbefore 3.5.9-150300.5.15.13.5.9-150300.5.15.1
openSUSE:Leap 15.4postfix-bdbbefore 3.5.9-150300.5.15.13.5.9-150300.5.15.1
openSUSE:Leap 15.5postfixbefore 3.7.3-150500.3.11.13.7.3-150500.3.11.1
openSUSE:Leap 15.5postfix-bdbbefore 3.7.3-150500.3.11.13.7.3-150500.3.11.1
openSUSE:Tumbleweedpostfixbefore 3.8.4-2.13.8.4-2.1
Red Hat:enterprise_linux:9::appstreampostfixbefore 2:3.5.25-1.el92:3.5.25-1.el9
Red Hat:enterprise_linux:9::appstreampostfix-cdbbefore 2:3.5.25-1.el92:3.5.25-1.el9
Red Hat:enterprise_linux:9::appstreampostfix-cdb-debuginfobefore 2:3.5.25-1.el92:3.5.25-1.el9
Red Hat:enterprise_linux:9::appstreampostfix-debuginfobefore 2:3.5.25-1.el92:3.5.25-1.el9
Red Hat:enterprise_linux:9::appstreampostfix-debugsourcebefore 2:3.5.25-1.el92:3.5.25-1.el9
Red Hat:enterprise_linux:9::appstreampostfix-ldapbefore 2:3.5.25-1.el92:3.5.25-1.el9
Red Hat:enterprise_linux:9::appstreampostfix-ldap-debuginfobefore 2:3.5.25-1.el92:3.5.25-1.el9

+17

Same product

postfix: all records

Other highest-scoring records for the same primary product.

  • CVE-2011-1720The SMTP server in Postfix before 2.5.13, 2.6.x before 2.6.10, 2.7.x before 2.7.4, and 2.8.x before 2.8.3, when certain Cyrus SASL…
    34Monitor
  • CVE-2011-0411The STARTTLS implementation in Postfix 2.4.x before 2.4.16, 2.5.x before 2.5.12, 2.6.x before 2.6.9, and 2.7.x before 2.7.3 does not…
    32Monitor
  • CVE-2017-10140Postfix before 2.11.10, 3.0.x before 3.0.10, 3.1.x before 3.1.6, and 3.2.x before 3.2.2 might allow local users to gain privileges by…
    31Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2012-0811Oct 1, 2014 · Multiple SQL injection vulnerabilities in Postfix Admin (aka postfixadmin) before 2.3.5 allow remote authenticated users to execute…
    27Monitor
  • ← EarlierCVE-2020-12063Apr 24, 2020 · A certain Postfix 2.10.1-7 package could allow an attacker to send an email from an arbitrary-looking sender via a homoglyph attack, as…
    21Monitor
  • Later →CVE-2026-43964May 4, 2026 · Postfix before 3.8.16, 3.9 before 3.9.10, and 3.10 before 3.10.9 sometimes allows a buffer over-read and process crash via an enhanced…
    30Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
almalinux:postfix2:3.5.25-1.el9 · AlmaLinux:9Package registry (OSV)
almalinux:postfix-cdb2:3.5.25-1.el9 · AlmaLinux:9Package registry (OSV)
almalinux:postfix-ldap2:3.5.25-1.el9 · AlmaLinux:9Package registry (OSV)
almalinux:postfix-lmdb2:3.5.25-1.el9 · AlmaLinux:9Package registry (OSV)
almalinux:postfix-mysql2:3.5.25-1.el9 · AlmaLinux:9Package registry (OSV)
almalinux:postfix-pcre2:3.5.25-1.el9 · AlmaLinux:9Package registry (OSV)
almalinux:postfix-perl-scripts2:3.5.25-1.el9 · AlmaLinux:9Package registry (OSV)
almalinux:postfix-pgsql2:3.5.25-1.el9 · AlmaLinux:9Package registry (OSV)
almalinux:postfix-sqlite2:3.5.25-1.el9 · AlmaLinux:9Package registry (OSV)
debian:postfix3.7.9-0+deb12u1 · Debian:12Package registry (OSV)
opensuse:postfix3.7.3-150500.3.11.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:postfix-bdb3.7.3-150500.3.11.1 · openSUSE:Leap 15.5Package registry (OSV)
red hat:postfix2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-cdb2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-cdb-debuginfo2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-debuginfo2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-debugsource2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-ldap2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-ldap-debuginfo2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-lmdb2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-lmdb-debuginfo2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-mysql2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-mysql-debuginfo2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
red hat:postfix-pcre2:3.5.25-1.el9 · Red Hat:enterprise_linux:9::appstreamPackage registry (OSV)
rocky linux:postfix2:3.5.25-1.el9 · Rocky Linux:9Package registry (OSV)
suse:postfix3.7.3-150500.3.11.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP5Package registry (OSV)
suse:postfix-bdb3.7.3-150500.3.11.1 · SUSE:Linux Enterprise Module for Legacy 15 SP5Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

  • Proof-of-concept repository on GitHub ×4

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHubstars:232023-12-26
Proof-of-concept repository on GitHubstars:42023-12-28
Proof-of-concept repository on GitHubstars:12023-12-31
Proof-of-concept repository on GitHubstars:02024-01-05

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. First PoC+2 d
  3. TodayNov 11, 2026+1053 d

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
low · data or configuration can be modified
Availability
none
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
Low
Availability impact
None

Weakness class (CWE)

CWE-345 · Insufficient Verification of Data Authenticity

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. SSVC exploitation— → none
  2. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (14 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records