Out-of-bounds Read in Exim
CVE-2026-40686
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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N.
EPSS exploit prediction
EPSS: 0.004 (32.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 32nd percentile — 32.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · 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/CVE2026-40686.assessment (Vendor Advisory)
- code.exim.org/exim/exim/commit/f2570bde16fb4d4a1242ff363a4c4eecf6372efc (Patch)
- exim.org/static/doc/security/CVE-2026-40686.txt (Broken Link)
Frequently asked questions
- What is CVE-2026-40686?
- CVE-2026-40686 is a low-severity vulnerability in Exim, classified under Out-of-bounds Read. CVSS score: 3.7/10. Published 2026-04-30.
- How severe is CVE-2026-40686?
- Low severity. CVSS v3 base score is 3.7 out of 10.