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Fencer Vulns
medium 5.3

CVE-2023-51766 json

Exim before 4.97.1 allows SMTP smuggling in certain PIPELINING/CHUNKING configurations.

published 2023-12-24 2 y ago modified 2026-06-17 4 mo ago also EUVD-2023-56455

cvss
5.3
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 65%
public exploits
0
none known

Summary

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.

Patch / fix

  • exim exim 4.97.1
  • exim4 Debian 12 4.96-15+deb12u4
  • exim4 Debian 14, Debian 13 4.97-3

debian advisories DEBIAN-CVE-2023-51766

  • exim4 Ubuntu 20.04 LTS 4.93-13ubuntu1.10
  • exim4 Ubuntu 22.04 LTS 4.95-4ubuntu2.5
  • exim4 Ubuntu Pro 14.04 LTS 4.82-3ubuntu2.4+esm9
  • exim4 Ubuntu Pro 16.04 LTS 4.86.2-2ubuntu2.6+esm6
  • exim4 Ubuntu Pro 18.04 LTS 4.90.1-1ubuntu1.10+esm3

ubuntu advisories UBUNTU-CVE-2023-51766

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • exim openSUSE Tumbleweed 4.97.1-1.1
  • exim Package Hub 15 SP5, openSUSE Leap 15.5 4.97.1-bp155.5.9.1

opensuse advisories openSUSE-SU-2024:13543-1openSUSE-SU-2024:0007-1

  • exim Alpine 3.24, Alpine 3.23, Alpine 3.22 +3 more 4.97.1-r0

alpine advisories ALPINE-CVE-2023-51766

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2023-51766 updated cvss 4.3

exim: SMTP smuggling vulnerability

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.10% chance of exploitation in the next 30 days, higher than 65% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • youtube.com https://www.youtube.com/watch?v=V8KPV96g1To referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Classification

Weakness
  • CWE-345 Insufficient Verification of Data Authenticity

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.