What is CVE-2026-40685?

CVE-2026-40685 is a medium-severity vulnerability in Exim, classified under CWE-684. CVSS score: 6.5/10. Published 2026-04-30.

How severe is CVE-2026-40685?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Buffer overflow in Exim

CVE-2026-40685

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.

EPSS: 0.001 (31.6th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H.

Affected products

Exim — versions 0

Weakness classification (CWE)

CWE-684
CWE-787 — Out-of-bounds Write

References

cve@mitre.org (Mailing List, Third Party Advisory)
cve@mitre.org (Vendor Advisory)
cve@mitre.org (Patch)
cve@mitre.org (Broken Link)

Frequently asked questions

What is CVE-2026-40685?: CVE-2026-40685 is a medium-severity vulnerability in Exim, classified under CWE-684. CVSS score: 6.5/10. Published 2026-04-30.
How severe is CVE-2026-40685?: Medium severity. CVSS v3 base score is 6.5 out of 10.