CVE-2023-51766: exim
Affects eximSource CVE Database V5
Not known to be exploited : upgrade to 4.97.1 soon.
Data as of 26 Oct 2026, 13:47 UTC
Rated High by the CNA (mitre) · No CVSS score from NVD or the CNA
- EPSS
- 1.1% chance of exploitation in 30 days – higher than 65% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 4.97.1
Exploitation evidence
Disclosed: evidence found.
CVE published 24 Dec 2023
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade exim/exim to 4.97.1.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
GitHubexim/eximpkg:github/exim/eximOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
Upgrade Exim to version 4.97.1 or later, where this vulnerability has been fixed. No other mitigation steps are indicated by the vendor advisory.
Description
Exim versions prior to 4.97.1 contain a vulnerability that allows SMTP smuggling in certain PIPELINING/CHUNKING configurations. This flaw enables remote attackers to inject email messages with a spoofed MAIL FROM address, potentially bypassing SPF protection mechanisms. The issue arises because Exim supports the sequence <LF>.<CR><LF>, which some other popular email servers do not handle correctly. A fix is available in Exim version 4.97.1.
References
- sec-consult.com/blog/detail/smtp-smuggling-spoofing-e-mails-worldwide/ (opens in a new tab)
- exim.org/static/doc/security/CVE-2023-51766.txt (opens in a new tab)
- bugs.exim.org/show_bug.cgi?id=3063 (opens in a new tab)
- openwall.com/lists/oss-security/2023/12/23/2 (opens in a new tab)
- openwall.com/lists/oss-security/2023/12/24/1 (opens in a new tab)
- openwall.com/lists/oss-security/2023/12/25/1 (opens in a new tab)
- git.exim.org/exim.git/commit/5bb786d5ad568a88d50d15452aacc8404047e5ca (opens in a new tab)
- git.exim.org/exim.git/commit/cf1376206284f2a4f11e32d931d4aade34c206c5 (opens in a new tab)
- bugzilla.redhat.com/show_bug.cgi?id=2255852 (opens in a new tab)
- fahrplan.events.ccc.de/congress/2023/fahrplan/events/11782.html (opens in a new tab)
- openwall.com/lists/oss-security/2023/12/29/2 (opens in a new tab)
- github.com/Exim/exim/blob/master/doc/doc-txt/cve-2023-51766 (opens in a new tab)
- openwall.com/lists/oss-security/2024/01/01/1 (opens in a new tab)
- openwall.com/lists/oss-security/2024/01/01/2 (opens in a new tab)
- openwall.com/lists/oss-security/2024/01/01/3 (opens in a new tab)
- youtube.com/watch?v=V8KPV96g1To (opens in a new tab)
- lists.debian.org/debian-lts-announce/2024/01/msg00002.html (opens in a new tab)
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/ (opens in a new tab)
- lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/ (opens in a new tab)
- lwn.net/Articles/956533/ (opens in a new tab)
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/ORN7OKEQPPBKUHYRQ6LR5PSNBQVDHAWB/ (opens in a new tab)
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QPDWHJPABVJCXDSNELSSVTIVAJU2MDUQ/ (opens in a new tab)