CVE-2026-40685

9.8 criticalEPSS 0.3%

Critical (9.8) in exim exim. EPSS 0.3% chance of exploitation in the next 30 days.

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.

Severity

CVSS 3.1

9.8 critical

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.3% chance of exploitation in the next 30 days; higher than 25% of CVEs (scores of 2026-10-31)
CWEs: CWE-787, CWE-684
Published: 2026-04-30
Modified: 2026-06-17
Record from: the NVD, synced 2026-10-19

Affected

exim:exim

References

https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57
https://exim.org/static/doc/security/CVE-2026-40685.txt
https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment
https://www.openwall.com/lists/oss-security/2026/04/30/21

Check your stack JSON