CVE-2026-40685

EUVD-2026-26443
In Exim before 4.99.2, when JSON lookup is enabled, an out-of-bounds heap write can occur when a JSON operator encounters malformed JSON in an untrusted header, because of an incorrect implementation of \ skipping.
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
mitreCNA
6.5 MEDIUM
NETWORK
HIGH
NONE
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
Base Score
CVSS 3.x
EPSS Score
Percentile: 14.82%
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
unimportant
bookworm (security)
unimportant
bullseye
unimportant
bullseye (security)
unimportant
forky
unimportant
sid
4.99.2-1
fixed
trixie
unimportant
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/9fdc057e71b87c87a0d3d2288b2810a0efaaba57
https://exim.org/static/doc/security/CVE-2026-40685.txt
https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment
https://www.openwall.com/lists/oss-security/2026/04/30/21