CVE-2023-51766

Exploitation

Not assessed. CISA has not published an exploitation assessment for this record, and it is not in the KEV catalog. That is an absence of assessment, not a finding of no risk.

SSVC decision

Not assessed by CISA

EPSS probability

1.10% probability of exploitation activity in the next 30 days.

EPSS percentile

Equal to or higher than the score of 65.5% of scored records. A rank, not a probability.

NVD base score

5.3 (CVSS v3.x), scored by the NVD independently of the CNA.

NVD CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

NVD analysis status

Modified. NVD last modified this record on 2026-06-17.

Red Hat severity

No Red Hat rating. Red Hat rates the CVEs that affect its products.

Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.

Published

2023-12-24 00:00Z2 YR AGO

Last updated

2025-11-04 18:21Z11 MO AGO

Reserved

2023-12-24

Assigning CNA

mitre

Record state

PUBLISHED

Severity

Not rated by the issuing CNA

CNA CVSS vector

Not published by the issuing CNA

Weaknesses

• CWE-345Insufficient Verification of Data AuthenticityClass

Data version

5.2

Document digest

a9f0ca10d4867b9f211d9ff83348a0cd584c7a8540e7dda8fbd8a4d70eeb358d

• sec-consult.comhttps://sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/
• exim.orghttps://exim.org/static/doc/security/CVE-2023-51766.txt
• bugs.exim.orghttps://bugs.exim.org/show_bug.cgi?id=3063
• www.openwall.comhttps://www.openwall.com/lists/oss-security/2023/12/23/2
• www.openwall.com[oss-security] 20231224 Re: Re: New SMTP smuggling attackhttp://www.openwall.com/lists/oss-security/2023/12/24/1mailing-list
• www.openwall.com[oss-security] 20231225 Re: Re: New SMTP smuggling attackhttp://www.openwall.com/lists/oss-security/2023/12/25/1mailing-list
• git.exim.orghttps://git.exim.org/exim.git/commit/5bb786d5ad568a88d50d15452aacc8404047e5ca
• git.exim.orghttps://git.exim.org/exim.git/commit/cf1376206284f2a4f11e32d931d4aade34c206c5
• bugzilla.redhat.comhttps://bugzilla.redhat.com/show_bug.cgi?id=2255852
• fahrplan.events.ccc.dehttps://fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html
• www.openwall.com[oss-security] 20231229 CVE-2023-51766: Exim: SMTP smugglinghttp://www.openwall.com/lists/oss-security/2023/12/29/2mailing-list
• github.comhttps://github.com/Exim/exim/blob/master/doc/doc-txt/cve-2023-51766
• www.openwall.com[oss-security] 20240101 Re: CVE-2023-51766: Exim: SMTP smugglinghttp://www.openwall.com/lists/oss-security/2024/01/01/1mailing-list
• www.openwall.com[oss-security] 20240101 Re: CVE-2023-51766: Exim: SMTP smugglinghttp://www.openwall.com/lists/oss-security/2024/01/01/2mailing-list
• www.openwall.com[oss-security] 20240101 Re: CVE-2023-51766: Exim: SMTP smugglinghttp://www.openwall.com/lists/oss-security/2024/01/01/3mailing-list
• www.youtube.comhttps://www.youtube.com/watch?v=V8KPV96g1To
• lists.debian.org[debian-lts-announce] 20240105 [SECURITY] [DLA 3708-1] exim4 security updatehttps://lists.debian.org/debian-lts-announce/2024/01/msg00002.htmlmailing-list
• lists.fedoraproject.orgFEDORA-2024-1ef6197a49https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/vendor-advisory
• lists.fedoraproject.orgFEDORA-2024-e0841c83bbhttps://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/vendor-advisory
• lwn.nethttps://lwn.net/Articles/956533/
• lists.fedoraproject.orghttps://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/
• lists.fedoraproject.orghttps://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/