CVE-2023-51765

CVE-2023-51765 is a medium-severity vulnerability in Sendmail with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-345.

Key facts

• Severity: Medium (CVSS 3.x base score 5.3)
• EPSS exploit prediction: 1% (61st percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-345
• Affected product: Sendmail
• Published: 2023-12-24
• Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2023-51765?

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.

How severe is CVE-2023-51765?

CVE-2023-51765 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2023-51765 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (61st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-51765?

CVE-2023-51765 primarily affects Sendmail. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2023-51765?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2023-51765 published?

CVE-2023-51765 was published on 2023-12-24 and last updated on 2026-06-17.

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
• https://lwn.net/Articles/956533/
• https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/
• https://www.openwall.com/lists/oss-security/2023/12/21/7
• https://www.openwall.com/lists/oss-security/2023/12/22/7
• https://www.youtube.com/watch?v=V8KPV96g1To

Affected products (4)

• cpe:2.3:a:sendmail:sendmail:*:*:*:*:*:*:*:*
• cpe:2.3:o:freebsd:freebsd:*:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
• cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:*

More vulnerabilities in Sendmail

• CVE-2003-0694 — Critical (CVSS 10.0): The prescan function in Sendmail 8.12.9 allows remote attackers to execute arbitrary code via buffer overflow attacks,…
• CVE-2003-0161 — Critical (CVSS 10.0): The prescan() function in the address parser (parseaddr.c) in Sendmail before 8.12.9 does not properly handle certain…
• CVE-2002-1337 — Critical (CVSS 10.0): Buffer overflow in Sendmail 5.79 to 8.12.7 allows remote attackers to execute arbitrary code via certain formatted…
• CVE-2007-2246 — High (CVSS 7.8): Unspecified vulnerability in HP-UX B.11.00 and B.11.11, when running sendmail 8.9.3 or 8.11.1; and HP-UX B.11.23 when…
• CVE-2006-0058 — High (CVSS 7.6): Signal handler race condition in Sendmail 8.13.x before 8.13.6 allows remote attackers to execute arbitrary code by…
• CVE-2009-4565 — High (CVSS 7.5): sendmail before 8.14.4 does not properly handle a '\0' character in a Common Name (CN) field of an X.509 certificate,…

All CVEs affecting Sendmail →

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