CVE-2023-51766: Exim: SMTP smuggling
First published: Sun Dec 24 2023(Updated: )
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.
Credit: cve@mitre.org cve@mitre.org
| Affected Software | Affected Version | How to fix |
|---|---|---|
| ubuntu/exim4 | <4.90.1-1ubuntu1.10+ | 4.90.1-1ubuntu1.10+ |
| ubuntu/exim4 | <4.93-13ubuntu1.10 | 4.93-13ubuntu1.10 |
| ubuntu/exim4 | <4.95-4ubuntu2.5 | 4.95-4ubuntu2.5 |
| ubuntu/exim4 | <4.96-17ubuntu2.2 | 4.96-17ubuntu2.2 |
| ubuntu/exim4 | <4.97-3 | 4.97-3 |
| ubuntu/exim4 | <4.97-3 | 4.97-3 |
| ubuntu/exim4 | <4.86.2-2ubuntu2.6+ | 4.86.2-2ubuntu2.6+ |
| debian/exim4 | 4.94.2-7+deb11u2 4.94.2-7+deb11u3 4.96-15+deb12u4 4.96-15+deb12u5 4.98-1 | |
| sa-exim | <4.97.1 | |
| Fedora EPEL | =7.0 | |
| Fedora EPEL | =8.0 | |
| Fedora EPEL | =9.0 | |
| Fedora | =38 | |
| Fedora | =39 | |
| Debian | =10.0 |
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Reference Links
- https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/
- https://exim.org/static/doc/security/CVE-2023-51766.txt
- https://bugs.exim.org/show_bug.cgi?id=3063
- https://www.openwall.com/lists/oss-security/2023/12/23/2
- http://www.openwall.com/lists/oss-security/2023/12/24/1
- http://www.openwall.com/lists/oss-security/2023/12/25/1
- https://git.exim.org/exim.git/commit/5bb786d5ad568a88d50d15452aacc8404047e5ca
- https://git.exim.org/exim.git/commit/cf1376206284f2a4f11e32d931d4aade34c206c5
- https://bugzilla.redhat.com/show_bug.cgi?id=2255852
- https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html
- http://www.openwall.com/lists/oss-security/2023/12/29/2
- https://github.com/Exim/exim/blob/master/doc/doc-txt/cve-2023-51766
- http://www.openwall.com/lists/oss-security/2024/01/01/1
- http://www.openwall.com/lists/oss-security/2024/01/01/2
- http://www.openwall.com/lists/oss-security/2024/01/01/3
- https://www.youtube.com/watch?v=V8KPV96g1To
- https://lists.debian.org/debian-lts-announce/2024/01/msg00002.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/
- https://lwn.net/Articles/956533/
- https://access.redhat.com/security/cve/CVE-2023-51766
- https://security-tracker.debian.org/tracker/CVE-2023-51766
- https://www.cve.org/CVERecord?id=CVE-2023-51766
- https://bugzilla.redhat.com/show_bug.cgi/show_bug.cgi?id=2255854
- https://bugzilla.redhat.com/show_bug.cgi/show_bug.cgi?id=2255853
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/
- https://launchpad.net/bugs/cve/CVE-2023-51766
- https://www.openwall.com/lists/oss-security/2023/12/21/6
- https://git.exim.org/exim.git/commit/4596719398f6f2365bed563aafd757a6433ce7b4
- https://ubuntu.com/security/notices/USN-6611-1
- https://nvd.nist.gov/vuln/detail/CVE-2023-51766
- https://ubuntu.com/security/CVE-2023-51766
Frequently Asked Questions
What is the severity of CVE-2023-51766?
CVE-2023-51766 is considered a high severity vulnerability due to its potential to allow remote attackers to bypass SPF mechanisms.
How do I fix CVE-2023-51766?
To fix CVE-2023-51766, upgrade Exim to version 4.97.1 or later.
Which versions of Exim are affected by CVE-2023-51766?
CVE-2023-51766 affects Exim versions prior to 4.97.1 across multiple operating systems including various Ubuntu and Debian releases.
Can CVE-2023-51766 allow unauthorized email sending?
Yes, CVE-2023-51766 can allow unauthorized email sending by enabling spoofed MAIL FROM addresses.
What mitigation measures can be taken against CVE-2023-51766?
In addition to upgrading Exim, implementing strict email validation and monitoring SMTP traffic can help mitigate CVE-2023-51766.
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