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    CVE-2023-51766

    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.

    Published:Dec 24, 2023
    Last Modified:Nov 4, 2025
    EPS:Dec 24, 2023
    EPSS Score:0.01642
    CVSS Score:5.3

    Affected Products

    Vendor
    Debian
    Product
    Debian Linux
    Vendor
    Exim
    Product
    Exim
    Vendor
    Fedoraproject
    Product
    Extra Packages For Enterprise Linux
    Vendor
    Fedoraproject
    Product
    Fedora

    Exploits

    https://www.youtube.com/watch?v=V8KPV96g1Tohttps://www.youtube.com/watch?v=V8KPV96g1To

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    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/2023/12/29/2
    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://bugs.exim.org/show_bug.cgi?id=3063
    https://bugzilla.redhat.com/show_bug.cgi?id=2255852
    https://exim.org/static/doc/security/CVE-2023-51766.txt
    https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html
    https://git.exim.org/exim.git/commit/5bb786d5ad568a88d50d15452aacc8404047e5ca
    https://git.exim.org/exim.git/commit/cf1376206284f2a4f11e32d931d4aade34c206c5
    https://github.com/Exim/exim/blob/master/doc/doc-txt/cve-2023-51766
    https://lists.debian.org/debian-lts-announce/2024/01/msg00002.html
    https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/
    https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/
    https://lwn.net/Articles/956533/
    https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/
    https://www.openwall.com/lists/oss-security/2023/12/23/2
    https://www.youtube.com/watch?v=V8KPV96g1To
    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/2023/12/29/2
    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://bugs.exim.org/show_bug.cgi?id=3063
    https://bugzilla.redhat.com/show_bug.cgi?id=2255852
    https://exim.org/static/doc/security/CVE-2023-51766.txt
    https://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html
    https://git.exim.org/exim.git/commit/5bb786d5ad568a88d50d15452aacc8404047e5ca
    https://git.exim.org/exim.git/commit/cf1376206284f2a4f11e32d931d4aade34c206c5
    https://github.com/Exim/exim/blob/master/doc/doc-txt/cve-2023-51766
    https://lists.debian.org/debian-lts-announce/2024/01/msg00002.html
    https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/
    https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/
    https://lists.fedoraproject.org/archives/list/[email protected]/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/
    https://lists.fedoraproject.org/archives/list/[email protected]/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/
    https://lwn.net/Articles/956533/
    https://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/
    https://www.openwall.com/lists/oss-security/2023/12/23/2
    https://www.youtube.com/watch?v=V8KPV96g1To

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High