What’s Vulnerable › Vulnerabilities

CVE-2023-51765

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.1% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2023-12-24 · updated 2026-06-17
• Weakness: CWE-345

Description

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.

Affected products

• FreeBSD: before 11.0 — fixed in 11.0
• Red Hat Enterprise Linux: 8.0, 9.0
• Sendmail: before 8.18.0.2 — fixed in 8.18.0.2

How to fix

Upgrade to a fixed version: FreeBSD 11.0; Sendmail 8.18.0.2. Check the vendor advisory for mitigations.

References

• http://www.openwall.com/lists/oss-security/2023/12/24/1
• http://www.openwall.com/lists/oss-security/2023/12/25/1
• http://www.openwall.com/lists/oss-security/2023/12/26/5
• http://www.openwall.com/lists/oss-security/2023/12/29/5
• http://www.openwall.com/lists/oss-security/2023/12/30/1
• http://www.openwall.com/lists/oss-security/2023/12/30/3
• https://access.redhat.com/security/cve/CVE-2023-51765
• https://bugzilla.redhat.com/show_bug.cgi?id=2255869
• https://bugzilla.suse.com/show_bug.cgi?id=1218351
• https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html
• https://github.com/freebsd/freebsd-src/commit/5dd76dd0cc19450133aa379ce0ce4a68ae07fb39#diff-afdf514b32ac88004952c11660c57bc96c3d8b2234007c1cbd8d7ed7fd7935cc
• https://lists.debian.org/debian-lts-announce/2024/06/msg00004.html

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