CVE-2025-11776 is a medium-severity (CVSS 4.3) CWE-863 vulnerability in github.com/mattermost/mattermost/server/v8. A fix is available for github.com/mattermost/mattermost/server/v8 — see the affected versions and patch details below.
Mattermost fails to properly restrict access to archived channel search API
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 CVE-2025-11776.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
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 < 11 fail to properly restrict access to archived channel search API which allows guest users to discover archived public channels via the /api/v4/teams/{team_id}/channels/search_archived endpoint
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost/server/v8 | all versions | 8.0.0-20250815165020-c8d66301415dgo get github.com/mattermost/mattermost/server/v8@v8.0.0-20250815165020-c8d66301415d |
| 🐹Go | github.com/mattermost/mattermost | all versions | 5.3.2-0.20250815165020-c8d66301415dgo get github.com/mattermost/mattermost@v5.3.2-0.20250815165020-c8d66301415d |
| 🐹Go | github.com/mattermost/mattermost-server | all versions | 5.3.2-0.20250815165020-c8d66301415dgo get github.com/mattermost/mattermost-server@v5.3.2-0.20250815165020-c8d66301415d |
| 🐹Go | github.com/mattermost/mattermost-server/v5 | all versions | 5.3.2-0.20250815165020-c8d66301415dgo get github.com/mattermost/mattermost-server/v5@v5.3.2-0.20250815165020-c8d66301415d |
| 🐹Go | github.com/mattermost/mattermost-server/v6 | all versions | 5.3.2-0.20250815165020-c8d66301415dgo get github.com/mattermost/mattermost-server/v6@v5.3.2-0.20250815165020-c8d66301415d |
Affected Products
mattermost servermattermostDetection & 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/v8, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/mattermost/mattermost/server/v8 to 8.0.0-20250815165020-c8d66301415d or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-11776 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
Frequently Asked Questions
Is CVE-2025-11776 in your dependencies?
Find it across Go, including transitive dependencies.