Mattermost doesn't enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler (CVE-2026-5139) | HOL Guard CVE

Medium · CVSS 5.4CVE-2026-5139GHSA-2G8V-GRQ3-HQ2G

Mattermost doesn't enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler

Answer in brief

CVE-2026-5139 records a Medium severity (CVSS 5.4) vulnerability in Mattermost doesn't enforce administrator authorization on the {{setDefaultInstance}} call within the {{/gitlab connect}} command handler. The current sources do not mark it as known exploited. The current feed maps github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Jun 22, 2026Updated Sep 15, 2026Source checked Sep 15, 2026First seen by HOL Jun 22, 2026Material review Sep 15, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 5.4
Exploitation: Not marked as known exploited
Affected software: 4 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 5.4. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go), github.com/mattermost/mattermost-server (go). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
github.com/mattermost/mattermost-servergo	>=11.7.0,<11.7.1	11.7.1
github.com/mattermost/mattermost-servergo	>=11.6.0,<11.6.3	11.6.3
github.com/mattermost/mattermost-servergo	>=11.5.0,<11.5.6	11.5.6
github.com/mattermost/mattermost-servergo	>=10.11.0,<10.11.18	10.11.18

Recommended response

Check inventory. Check lockfiles and deployed manifests for github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server.
Review the reported fix. Update github.com/mattermost/mattermost-server to 11.7.1; github.com/mattermost/mattermost-server to 11.6.3; github.com/mattermost/mattermost-server to 11.5.6; github.com/mattermost/mattermost-server to 10.11.18 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Jun 22, 2026
Evidence: source:ghsa:source_dates:source-dates:record
Source modified
Sep 15, 2026
Evidence: source:ghsa:source_dates:source-dates:record
First seen by HOL
Jun 22, 2026

Sources and claim methodology

Upstream source 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

Quoted source text, attributed separately from HOL analysis.