CVE-2023-51764

MEDIUMNVD 5.35.3—
EchelonGraph scoreMEDIUM confidence

Score 5.3 from GitHub Security Advisory published 2023-12-24. NVD baseline CVSS 5.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Elevated
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 3%CVSS: 5.3Exploit: Elevated riskExposed: 0

A fix is available — apply it.

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.

CVSS v3
5.3
EG Score
5.3(medium)
EG Risk
44(Track)
EG Risk 44/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity53% × 45%
Exploitation40% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
3%
EPSS %ILE
85%
KEV
Not listed

Published

December 24, 2023

Last Modified

June 17, 2026

References (36)

Vendor Advisories for CVE-2023-51764(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(3)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntupostfix-pgsql (3.1.0-3ubuntu0.4+esm2) @ xenial2026-05-24ubuntu
ubuntupostfix-sqlite (3.4.13-0ubuntu1.4) @ focal2026-05-24ubuntu
redhatpostfix-2:3.5.25-1.el92024-11-12redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(5 across 5 ecosystems)
Debian:10(1)
PackageVulnerable rangeFixed inDependents
postfix3.4.10-0+deb10u1 ... 3.4.9-1 (12 versions)3.4.23-0+deb10u2—
Debian:11(1)
PackageVulnerable rangeFixed inDependents
postfix3.5.13-0+deb11u1, 3.5.13-1, 3.5.17-0+deb11u1, 3.5.18-0+deb11u1, 3.5.6-13.5.23-0+deb11u1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
postfix3.7.5-2, 3.7.6-0+deb12u1, 3.7.6-0+deb12u23.7.9-0+deb12u1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
postfix—3.8.4-1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
postfix—3.8.4-1—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Additional Vendor Advisories

(3)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 5× in last 7d / 30× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 158 total refreshes for this CVE.

  1. 2026-09-18 19:26 UTCEPSS rescore
  2. 2026-09-17 19:25 UTCEPSS rescore
  3. 2026-09-16 14:06 UTCEPSS rescore
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  16. 2026-09-03 09:30 UTCOSV refresh
  17. 2026-09-02 14:10 UTCEPSS rescore
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  1. 2026-08-25 13:46 UTCEPSS rescore
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  6. 2026-08-19 17:02 UTCEPSS rescore
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  8. 2026-08-18 13:46 UTCEPSS rescore
  9. 2026-08-17 13:45 UTCEPSS rescore
  10. 2026-08-16 22:56 UTCOSV refresh
  11. 2026-08-16 14:54 UTCEPSS rescore
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  23. 2026-08-05 19:15 UTCEPSS rescore
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  25. 2026-08-04 10:35 UTCEPSS rescore
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  28. 2026-08-02 02:25 UTCEPSS rescore
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  30. 2026-08-01 17:06 UTCOSV refresh
  31. 2026-08-01 04:14 UTCEPSS rescore
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  42. 2026-07-23 14:16 UTCEPSS rescore
  43. 2026-07-23 02:29 UTCEG score recompute
  44. 2026-07-22 23:15 UTCEG score recompute
  45. 2026-07-22 14:06 UTCEPSS rescore
  46. 2026-07-21 15:23 UTCEPSS rescore
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  48. 2026-07-20 17:06 UTCEPSS rescore
  49. 2026-07-19 14:29 UTCEPSS rescore
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  51. 2026-07-19 02:27 UTCEPSS rescore
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  54. 2026-07-16 17:01 UTCEPSS rescore
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  57. 2026-07-15 01:59 UTCEPSS rescore
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  59. 2026-07-15 00:10 UTCOSV refresh
  60. 2026-07-13 22:28 UTCEPSS rescore
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  64. 2026-07-12 05:45 UTCEPSS rescore
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  67. 2026-07-08 15:13 UTCEPSS rescore
  68. 2026-07-07 13:44 UTCEPSS rescore
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Publicly available exploits

(2 references)

Working exploit code is in the public domain (2 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCeeenvik1/CVE-2023-51764
    First seen Dec 28, 2023

    PoC CVE-2023-51764

    Open source ↗
  • GitHub PoCduy-31/CVE-2023-51764
    First seen Dec 26, 2023

    Postfix SMTP Smuggling - Expect Script POC

    Open source ↗

Frequently asked(5)

What is CVE-2023-51764?
CVE-2023-51764 is a medium vulnerability published on December 24, 2023. Postfix through 3.8.5 allows SMTP smuggling unless configured with smtpddatarestrictions=rejectunauthpipelining and smtpddiscardehlokeywords=chunking (or certain other options that exist in recent versions). Remote attackers can use a published exploitation technique to inject e-mail messages with…
When was CVE-2023-51764 disclosed?
CVE-2023-51764 was first published in the National Vulnerability Database on December 24, 2023, with the most recent update on June 17, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2023-51764 actively exploited?
CVE-2023-51764 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 3% probability of exploitation in the next 30 days, which ranks it in the top 15.1% of all scored CVEs.
What is the CVSS score of CVE-2023-51764?
CVE-2023-51764 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2023-51764?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2023-51764, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2023-51764

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