CVE-2023-51764
MEDIUMEPSS 85th pctlDescription
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.
How to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Exploit Intelligence
Elevated risk: more likely to be exploited than 85% of all known CVEs.
References
Related Vulnerabilities
Other CWE-345 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2023-38831 | High | 7.8 | 98% | KEV + Ransom | Fix |
| CVE-2016-4553 | High | 8.6 | 80% | - | Fix |
| CVE-2016-4554 | High | 8.6 | 39% | - | Fix |
| CVE-2023-35719 | Medium | 6.8 | 26% | - | - |
| CVE-2022-26871 | Critical | 9.8 | 20% | KEV | - |
| CVE-2014-4936 | High | 9.3 | 17% | - | - |
Common questions
How do I fix CVE-2023-51764?
Published advisories record a fix for 57 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2023-51764 being actively exploited?
Not that we know of. CVE-2023-51764 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 2.6% is the estimated probability that it will be exploited in the next 30 days. That is higher than 85% of all scored CVEs.
How severe is CVE-2023-51764?
CVE-2023-51764 has a CVSS v3 base score of 5.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2023-51764 affect?
Published advisories record a fix for postfix (Amazon), postfix-cdb (Amazon), postfix-cdb-debuginfo (Amazon), postfix-debuginfo (Amazon), and 53 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-17.