Vulnerability · Published Apr 30, 2026 · Assigned by mitre
CVE-2026-40684
Medium 5.9
In plain English
A medium-severity security flaw in Exim from Exim. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 30% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)5.9Medium
Exploit odds (30 days)0.4%top 69.8% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.23 | exim | 4.98.2-r0 | ALPINE-CVE-2026-40684 |
| Alpine:v3.24 | exim | 4.98.2-r0 | ALPINE-CVE-2026-40684 |
| Debian:12 | exim4 | 4.96-15+deb12u9 | DEBIAN-CVE-2026-40684 |
| Debian:13 | exim4 | 4.98.2-1+deb13u2 | DEBIAN-CVE-2026-40684 |
| Debian:14 | exim4 | 4.99.2-1 | DEBIAN-CVE-2026-40684 |
Affected products (as reported)
Weakness: CWE-684 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
References
- https://www.openwall.com/lists/oss-security/2026/04/30/21
- https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40684.assessment
- https://code.exim.org/exim/exim/commit/628bbaca7672748d941a12e7cd5f0122a4e18c81
- https://exim.org/static/doc/security/CVE-2026-40684.txt
- http://www.openwall.com/lists/oss-security/2026/05/01/11