Out-of-bounds Heap Write Vulnerability in Exim Email Server
CVE-2026-40685

6.5MEDIUM

Key Information:

Vendor

Exim

Status
Exim
Vendor
CVE Published:
30 April 2026

What is CVE-2026-40685?

A vulnerability in Exim prior to version 4.99.2 can lead to an out-of-bounds heap write when JSON lookup is enabled. This occurs due to improper handling of malformed JSON data in untrusted headers, resulting from incorrect implementation of escape character processing. Exploiting this vulnerability may allow an attacker to manipulate the server's memory, potentially leading to arbitrary code execution or denial of service.

Affected Version(s)

Exim 0 < 4.99.2

References

https://www.openwall.com/lists/oss-security/2026/04/30/21
https://exim.org/static/doc/security/cve-2026-04.1/CVE202...
https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0...

CVSS V3.1

Score:
6.5
Severity:
MEDIUM
Confidentiality:
None
Integrity:
Low
Availability:
None
Attack Vector:
Network
Attack Complexity:
High
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.