CVE-2026-40685 PUBLISHED

Assigner: mitre
Reserved: 14.04.2026 Published: 30.04.2026 Updated: 01.05.2026

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.

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H
CVSS Score: 6.5

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	None
Privileges Required	None	Integrity Impact	Low
User Interaction	None	Availability Impact	High

CVSS 3.1

Product Status

Vendor	Exim
Product	Exim
Versions	Default: unaffected affected from 0 to 4.99.2 (excl.)

References

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

Problem Types

CWE-684 Incorrect Provision of Specified Functionality CWE