CVE-2026-4915: Server panic via outgoing webhook responses

Published May 25, 2026
·
Updated

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

Affected Software

1 affected component
Mattermost Mattermost Server<=11.6.0, <=11.5.3, <=11.4.4, <=10.11.14

Remediation

Information

Update Mattermost to versions 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15 or higher.

Event History

May 25, 2026
CVE Published
via MITRE·07:10 AM
Data Sourced
via MITRE·07:10 AM
RemedyDescriptionSeverityWeakness
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Frequently Asked Questions

1

What is the severity of CVE-2026-4915?

CVE-2026-4915 has a medium severity score of 6.5.

2

How do I fix CVE-2026-4915?

To fix CVE-2026-4915, update Mattermost to versions 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15 or higher.

3

What does CVE-2026-4915 affect?

CVE-2026-4915 affects versions of Mattermost Server including 11.6.x, 11.5.x, 11.4.x, and 10.11.x.

4

What type of vulnerability is CVE-2026-4915?

CVE-2026-4915 is a denial of service vulnerability caused by server panic from unfiltered outgoing webhook responses.

5

Who is impacted by CVE-2026-4915?

Authenticated users of vulnerable Mattermost versions can exploit CVE-2026-4915 leading to server process termination.

Company

Resources

Contact

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