CVE-2026-5139
Received Received - Intake
Authorization Bypass in Mattermost GitLab Integration

Publication date: 2026-06-22

Last updated on: 2026-06-22

Assigner: Mattermost, Inc.

Description
Mattermost versions 11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17 fail to enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler, which allows any authenticated user to overwrite the global default GitLab instance configuration via the {{/gitlab connect <instance-name>}} slash command.. Mattermost Advisory ID: MMSA-2026-00644
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Meta Information
Published
2026-06-22
Last Modified
2026-06-22
Generated
2026-06-22
AI Q&A
2026-06-22
EPSS Evaluated
N/A
NVD
CVE-2026-5139
EUVD
EUVD-2026-38246
Affected Vendors & Products
Showing 4 associated CPEs
Vendor Product Version / Range
mattermost mattermost to 11.7.0 (inc)
mattermost mattermost to 11.6.2 (inc)
mattermost mattermost to 11.5.5 (inc)
mattermost mattermost to 10.11.17 (inc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-862 The product does not perform an authorization check when an actor attempts to access a resource or perform an action.
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Executive Summary

This vulnerability exists in certain versions of Mattermost (11.7.x <= 11.7.0, 11.6.x <= 11.6.2, 11.5.x <= 11.5.5, 10.11.x <= 10.11.17) where the system fails to enforce administrator authorization on the setDefaultInstance call within the /gitlab connect command handler.

Because of this failure, any authenticated user can overwrite the global default GitLab instance configuration by using the /gitlab connect <instance-name> slash command.

Impact Analysis

This vulnerability allows any authenticated user to change the global default GitLab instance configuration without requiring administrator privileges.

Such unauthorized changes could lead to potential misconfigurations, impacting the integrity and availability of the GitLab integration within Mattermost.

The CVSS score of 5.4 indicates a medium severity with low attack complexity but requiring privileges, and it can cause integrity and availability impacts.

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