CVE-2026-4915

Name: CVE-2026-4915
Creator: NVD / NIST
Published: 2026-05-25T08:16:24.897+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 0.28%

Last modified Jun 17, 2026

CVE-2026-4915 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry.. Mattermost Advisory ID: MMSA-2026-00641. EPSS estimates a 0.28% chance of exploitation in the next 30 days.

Description

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry.. Mattermost Advisory ID: MMSA-2026-00641

Metrics

CVSS 3.1

6.5/10

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

EPSS Probability

0.28%

19.4th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-754

Affected Software

Vendor	Product	Versions
Mattermost	Mattermost Server	>= 10.11.0, < 10.11.15
Mattermost	Mattermost Server	>= 11.4.0, < 11.4.5
Mattermost	Mattermost Server	>= 11.5.0, < 11.5.4
Mattermost	Mattermost Server	>= 11.6.0, < 11.6.1

References

https://mattermost.com/security-updatesVendor Advisory

Timeline

Published: May 25, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-4915?

How severe is CVE-2026-4915?

CVE-2026-4915 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.28% probability of exploitation in the next 30 days.

How do I fix CVE-2026-4915?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-4915?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST