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Fencer Intel
low 3.7

CVE-2026-40686 json

In Exim before 4.99.2, when utf8 operators are enabled, there is an out-of-bounds read if large UTF-8 trailing characters are present (malf…

published 6mo ago modified 4mo ago also EUVD-2026-26444

cvss
3.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 15%
public exploits
0
none known

Summary

In Exim before 4.99.2, when utf8 operators are enabled, there is an out-of-bounds read if large UTF-8 trailing characters are present (malformed UTF-8 header data). Information might be divulged within an error message produced during handling of an unrelated e-mail message.

Patch / fix

  • Exim Exim 4.99.2
  • exim4 Debian 12 4.96-15+deb12u9
  • exim4 Debian 13 4.98.2-1+deb13u2
  • exim4 Debian 14 4.99.2-1

debian advisories DEBIAN-CVE-2026-40686

  • exim4 Ubuntu 22.04 LTS 4.95-4ubuntu2.7
  • exim4 Ubuntu 24.04 LTS 4.97-4ubuntu4.4
  • exim4 Ubuntu 25.10 4.98.2-1ubuntu2.1
  • exim4 Ubuntu 26.04 LTS 4.99.1-1ubuntu1.1
  • exim4 Ubuntu Pro 20.04 LTS 4.93-13ubuntu1.12+esm1

ubuntu advisories UBUNTU-CVE-2026-40686

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 Alpine 3.24, Alpine 3.23 4.98.2-r0

alpine advisories ALPINE-CVE-2026-40686

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

Is CVE-2026-40686 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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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-2026-40686 updated cvss 3.7

Exim: Exim: Information disclosure via malformed UTF-8 header data

  • 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

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
6mo ago

Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 15% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Affected products

  • Exim Exim

Classification

Weakness

References

Sources

Fencer Intel 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.