CVE-2026-4915
Analyzed Analyzed - Analysis Complete
Denial of Service in Mattermost via Null Webhook Attachments

Publication date: 2026-05-25

Last updated on: 2026-06-01

Assigner: Mattermost, Inc.

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
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Meta Information
Published
2026-05-25
Last Modified
2026-06-01
Generated
2026-06-15
AI Q&A
2026-05-26
EPSS Evaluated
2026-06-14
NVD
CVE-2026-4915
EUVD
EUVD-2026-31646
Affected Vendors & Products
Showing 4 associated CPEs
Vendor Product Version / Range
mattermost mattermost_server From 10.11.0 (inc) to 10.11.15 (exc)
mattermost mattermost_server From 11.4.0 (inc) to 11.4.5 (exc)
mattermost mattermost_server From 11.5.0 (inc) to 11.5.4 (exc)
mattermost mattermost_server From 11.6.0 (inc) to 11.6.1 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-754 The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.
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Executive Summary

This vulnerability affects certain versions of Mattermost where the software fails to filter out nil (null) elements from outgoing webhook attachment payloads before processing them.

An authenticated user can exploit this by sending a specially crafted webhook callback response that contains a null attachment entry.

This causes the server process to terminate unexpectedly, resulting in a denial of service.

Impact Analysis

The primary impact of this vulnerability is a denial of service (DoS) condition.

An attacker who is authenticated can cause the Mattermost server process to terminate by sending a crafted webhook callback response with a null attachment.

This can disrupt normal operations, causing downtime and potentially affecting availability of the Mattermost service.

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