Vulnerability in Exim
CVE-2026-40684
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.006 (48.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 48th percentile — 48.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.006 · change: +0.002
Affected products
- Exim — versions 0
Weakness classification (CWE)
References
- www.openwall.com/lists/oss-security/2026/04/30/21 (Mailing List, Third Party Advisory)
- exim.org/static/doc/security/cve-2026-04.1/CVE2026-40684.assessment (Vendor Advisory)
- code.exim.org/exim/exim/commit/628bbaca7672748d941a12e7cd5f0122a4e18c81 (Patch)
- exim.org/static/doc/security/CVE-2026-40684.txt (Broken Link)
- af854a3a-2127-422b-91ae-364da2661108
Frequently asked questions
- What is CVE-2026-40684?
- CVE-2026-40684 is a medium-severity vulnerability in Exim, classified under CWE-684. CVSS score: 5.9/10. Published 2026-04-30.
- How severe is CVE-2026-40684?
- Medium severity. CVSS v3 base score is 5.9 out of 10.