CVE-2026-40685
Exim JSON Heap Write Vulnerability
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.
INFO
Published Date :
April 30, 2026, 10:16 p.m.
Last Modified :
May 1, 2026, 5:51 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | 8254265b-2729-46b6-b9e3-3dfca2d5bfca | ||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | MEDIUM | MITRE-CVE | ||||
| CVSS 3.1 | CRITICAL | [email protected] |
Solution
- Update Exim to version 4.99.2 or later.
- Disable JSON lookup if update is not possible.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-40685.
| URL | Resource |
|---|---|
| https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57 | Patch |
| https://exim.org/static/doc/security/CVE-2026-40685.txt | Broken Link |
| https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment | Vendor Advisory |
| https://www.openwall.com/lists/oss-security/2026/04/30/21 | Mailing List Third Party Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-40685 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-40685
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-40685 vulnerability anywhere in the article.
-
CybersecurityNews
Multiple Exim Mail Server Vulnerabilities Leads to Crash with Malicious DNS data
The Exim development team has released version 4.99.2 to address four newly discovered security vulnerabilities affecting their mail server software. These flaws allow attackers to potentially crash s ... Read more
The following table lists the changes that have been made to the
CVE-2026-40685 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
May. 01, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Added CWE CWE-787 Added CPE Configuration OR *cpe:2.3:a:exim:exim:*:*:*:*:*:*:*:* versions up to (excluding) 4.99.2 Added Reference Type MITRE: https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57 Types: Patch Added Reference Type MITRE: https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment Types: Vendor Advisory Added Reference Type MITRE: https://exim.org/static/doc/security/CVE-2026-40685.txt Types: Broken Link Added Reference Type MITRE: https://www.openwall.com/lists/oss-security/2026/04/30/21 Types: Mailing List, Third Party Advisory -
CVE Modified by [email protected]
May. 01, 2026
Action Type Old Value New Value Added Reference https://exim.org/static/doc/security/CVE-2026-40685.txt Removed Reference https://exim.org/static/doc/security/CVE-2025-40685.txt -
New CVE Received by [email protected]
Apr. 30, 2026
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H Added CWE CWE-684 Added Reference https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57 Added Reference https://exim.org/static/doc/security/CVE-2025-40685.txt Added Reference https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment Added Reference https://www.openwall.com/lists/oss-security/2026/04/30/21