Mattermost <=11.7.0/11.6.2/11.5.5/10.11.17 Auth Bypass on /gitlab connect
CVE-2026-5139 Published on June 22, 2026

GitLab Plugin Allows Non-Admin Users to Modify Default Instance Configuration
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

Vendor Advisory NVD

Vulnerability Analysis

CVE-2026-5139 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, with no impact on integrity and availability.

Attack Vector:
NETWORK
Attack Complexity:
LOW
Privileges Required:
LOW
User Interaction:
NONE
Scope:
UNCHANGED
Confidentiality Impact:
NONE
Integrity Impact:
LOW
Availability Impact:
LOW

Weakness Type

What is an AuthZ Vulnerability?

The software does not perform an authorization check when an actor attempts to access a resource or perform an action.

CVE-2026-5139 has been classified to as an AuthZ vulnerability or weakness.


Products Associated with CVE-2026-5139

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Affected Versions

Mattermost: