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CVE-2023-51765

MediumPublished

sendmail through 8.17.2 allows SMTP smuggling in certain configurations. Remote attackers can use a published exploitation technique to inject e-mail...

Published: Dec 24, 2023
Updated: Aug 2, 2024
Assigning CNA: mitre
Evidence observed: Aug 8, 2026

Primary CVSS

5.3/ 10Medium

nvd · CVSS 3.1

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

EPSS probability estimate

1.1%

Low · next 30 days

Percentile: 63.3%
Model date: Sep 21, 2026

EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.

Summary

sendmail through 8.17.2 allows SMTP smuggling in certain configurations. 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 sendmail supports <LF>.<CR><LF> but some other popular e-mail servers do not. This is resolved in 8.18 and later versions with 'o' in srv_features.

Sources

CVE-2023-51764PoC
Proof-of-concept exploit for CVE-2023-51764 SMTP smuggling vulnerability in Postfix, enabling email spoofing and message injection via crafted SMTP sessions.

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