CVE-2026-40685

critical

Description

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.

References

https://www.openwall.com/lists/oss-security/2026/04/30/21

https://seclists.org/oss-sec/2026/q2/306

https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment

https://exim.org/static/doc/security/CVE-2026-40685.txt

https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57

Details

Source: Mitre, NVD

Published: 2026-04-30

Updated: 2026-05-01

Risk Information

CVSS v2

Base Score: 10

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C

Severity: Critical

CVSS v3

Base Score: 9.8

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