CVE-2026-40685

Publication date 29 April 2026

Last updated 2 June 2026

Ubuntu priority

Cvss 3 Severity Score

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.

Read the notes from the security team

Status

Show unmaintained releases

Package	Ubuntu Release	Status
exim4	26.04 LTS resolute	Fixed 4.99.1-1ubuntu1.1
	25.10 questing	Fixed 4.98.2-1ubuntu2.1
	24.04 LTS noble	Fixed 4.97-4ubuntu4.4
	22.04 LTS jammy	Fixed 4.95-4ubuntu2.7
	20.04 LTS focal	Vulnerable
	18.04 LTS bionic	Ignored changes too intrusive
	16.04 LTS xenial	Ignored end of ESM support, was needs-triage
	14.04 LTS trusty	Ignored changes too intrusive

Notes

kkernick

Bionic and below require f3ebb786e451da973560f1c9d8cdb151d25108b5 which introduces over 3000 LoC

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package	Patch details
exim4	Upstream: ecf4e26

Severity score breakdown

Parameter	Value
Base score	6.5 · Medium
Attack vector	Network
Attack complexity	High
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	None
Integrity impact	Low
Availability impact	High
Vector	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H

References

Related Ubuntu Security Notices (USN)

USN-8228-1
Exim vulnerabilities
4 May 2026