CVE-2026-5139

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

Score

CVSS 3.1 5.4 Medium

Status

Analyzed - responsibledisclosure@mattermost.com

Published

2026-06-22

Last modified

2026-06-22

Weaknesses

CWE-862

Affected products

• Mattermost (Mattermost)
• Mattermost Server (Mattermost)

References

• https://mattermost.com/security-updates