CVE-2023-51766

moderate-risk

Published 2023-12-24

Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING 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 Exim supports <LF>.<CR><LF> but some other popular e-mail servers do not.

Do I need to act?

1.6% chance of exploitation in next 30 days

EPSS score — moderate exploit probability

Not on CISA KEV list

No confirmed active exploitation reported to CISA

Patch status unknown

Check vendor advisories for fix availability and mitigation guidance

CVSS 5.3/10 Medium

NETWORK / LOW complexity

Affected Products (7)

Exim

Extra Packages For Enterprise Linux

Fedora

Debian Linux

Affected Vendors

Debian Fedoraproject Exim

References (42)

Mailing List http://www.openwall.com/lists/oss-security/2023/12/24/1

Mailing List http://www.openwall.com/lists/oss-security/2023/12/25/1

Mailing List http://www.openwall.com/lists/oss-security/2023/12/29/2

Mailing List http://www.openwall.com/lists/oss-security/2024/01/01/1

Mailing List http://www.openwall.com/lists/oss-security/2024/01/01/2

Mailing List http://www.openwall.com/lists/oss-security/2024/01/01/3

Issue Tracking https://bugs.exim.org/show_bug.cgi?id=3063

Issue Tracking https://bugzilla.redhat.com/show_bug.cgi?id=2255852

Broken Link https://exim.org/static/doc/security/CVE-2023-51766.txt

Technical Description https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html

Patch https://git.exim.org/exim.git/commit/5bb786d5ad568a88d50d15452aacc8404047e5ca

Patch https://git.exim.org/exim.git/commit/cf1376206284f2a4f11e32d931d4aade34c206c5

Mitigation https://github.com/Exim/exim/blob/master/doc/doc-txt/cve-2023-51766

Mailing List https://lists.debian.org/debian-lts-announce/2024/01/msg00002.html

Mailing List https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedorapro...

Third Party Advisory https://lwn.net/Articles/956533/

Technical Description https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/

Issue Tracking https://www.openwall.com/lists/oss-security/2023/12/23/2

Exploit https://www.youtube.com/watch?v=V8KPV96g1To

and 22 more references

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moderate-risk

Severity 21/34 · High

Exploitability 4/34 · Minimal

Exposure 14/34 · Moderate