GHSA-mqcj-8c2g-h97q is a low-severity (CVSS 3.1) CWE-863 vulnerability in github.com/mattermost/mattermost-server. A fix is available for github.com/mattermost/mattermost-server — see the affected versions and patch details below.
Mattermost Incorrect Authorization vulnerability
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-mqcj-8c2g-h97q.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-mqcj-8c2g-h97q plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server/v5🐹github.com/mattermost/mattermost-server/v6Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Mattermost versions 10.11.x <= 10.11.3, 10.5.x <= 10.5.11 fail to properly validate team membership permissions in the Add Channel Member API, which allows users from one team to access user metadata and channel membership information from other teams via the API endpoint.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.11.0&&< 10.11.4 | 10.11.4go get github.com/mattermost/mattermost-server@v10.11.4 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.5.0&&< 10.5.12 | 10.5.12go get github.com/mattermost/mattermost-server@v10.5.12 |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | all versions | 8.0.0-20250905150616-ba86dfc5876bgo get github.com/mattermost/mattermost/server/v8@v8.0.0-20250905150616-ba86dfc5876b |
| 🐹Go | github.com/mattermost/mattermost | all versions | 5.3.2-0.20250905150616-ba86dfc5876bgo get github.com/mattermost/mattermost@v5.3.2-0.20250905150616-ba86dfc5876b |
| 🐹Go | github.com/mattermost/mattermost-server | all versions | 5.3.2-0.20250905150616-ba86dfc5876bgo get github.com/mattermost/mattermost-server@v5.3.2-0.20250905150616-ba86dfc5876b |
| 🐹Go | github.com/mattermost/mattermost-server/v5 | all versions | 5.3.2-0.20250905150616-ba86dfc5876bgo get github.com/mattermost/mattermost-server/v5@v5.3.2-0.20250905150616-ba86dfc5876b |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/mattermost/mattermost-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/mattermost/mattermost-server to 10.11.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mqcj-8c2g-h97q is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-mqcj-8c2g-h97q can be triaged on real exposure rather than presence alone.
Tailored to GHSA-mqcj-8c2g-h97q. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-mqcj-8c2g-h97q in your dependencies?
O3 Security finds GHSA-mqcj-8c2g-h97q across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.