Medium severity · published Jun 22, 2026
CVE-2026-5139
GitLab Plugin Allows Non-Admin Users to Modify Default Instance Configuration
5.4
CVSS
0.3%
EPSS
No
On KEV
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
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
Low
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 21% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.7.0 through 11.7.0; 11.6.0 through 11.6.2; 11.5.0 through 11.5.5; 10.11.0 through 10.11.17 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.18; 11.5.0 before 11.5.6; 11.6.0 before 11.6.3; 11.7.0 before 11.7.1 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-5139
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-5139
Vendor Advisory
https://mattermost.com/security-updates
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