CVE-2026-40686

EUVD-2026-26444
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.
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
mitreCNA
3.7 LOW
NETWORK
HIGH
NONE
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
Base Score
CVSS 3.x
EPSS Score
Percentile: 8.16%
Early Detection
Affected products identified ahead of NVD analysis through intelligence sources.
VendorProductVersionSource
eximexim
𝑥
< 4.99.2
CNA
Debian logo
Debian Releases
Debian Product
Codename
exim4
bookworm
vulnerable
bookworm (security)
vulnerable
bullseye
vulnerable
bullseye (security)
vulnerable
forky
vulnerable
sid
4.99.2-1
fixed
trixie
vulnerable
Ubuntu logo
Ubuntu Releases
Ubuntu Product
Codename
exim4
bionic
needs-triage
focal
needs-triage
jammy
needs-triage
noble
needs-triage
questing
needs-triage
resolute
needs-triage
trusty
needs-triage
xenial
needs-triage
Common Weakness Enumeration
References
https://code.exim.org/exim/exim/commit/f2570bde16fb4d4a1242ff363a4c4eecf6372efc
https://exim.org/static/doc/security/CVE-2026-40686.txt
https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40686.assessment
https://www.openwall.com/lists/oss-security/2026/04/30/21