CVE-2026-40684

EUVD-2026-26442
In Exim before 4.99.2, on systems using musl libc (not glibc), an attacker can crash the connection instance when malformed DNS data is present in PTR records. This is caused by a dn_expand oddity in octal printing.
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
mitreCNA
5.9 MEDIUM
NETWORK
HIGH
NONE
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/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
not-affected
focal
not-affected
jammy
not-affected
noble
not-affected
questing
not-affected
resolute
not-affected
trusty
not-affected
xenial
not-affected
Common Weakness Enumeration
References
https://code.exim.org/exim/exim/commit/628bbaca7672748d941a12e7cd5f0122a4e18c81
https://exim.org/static/doc/security/CVE-2026-40684.txt
https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40684.assessment
https://www.openwall.com/lists/oss-security/2026/04/30/21