GHSA-q453-638c-h4mr
MEDIUMGHSA-q453-638c-h4mr is a medium-severity (CVSS 6.8) Unrestricted File Upload vulnerability in github.com/mattermost/mattermost-server. O3 Security confirms whether GHSA-q453-638c-h4mr is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Mattermost Fails to Validate Remote Cluster Upload Sessions
Blast Radius
github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost/server/v8🐹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 10.8.x <= 10.8.3, 10.5.x <= 10.5.8, 9.11.x <= 9.11.17, 10.9.x <= 10.9.2, 10.10.x <= 10.10.0 fail to validate upload types in remote cluster upload sessions which allows a system admin to upload non-attachment file types via shared channels that could potentially be placed in arbitrary filesystem directories.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.8.0&&< 10.8.4 | 10.8.4 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.5.0&&< 10.5.9 | 10.5.9 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 9.11.0&&< 9.11.18 | 9.11.18 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.9.0&&< 10.9.3 | 10.9.3 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.10.0&&< 10.10.1 | 10.10.1 |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | all versions | 8.0.0-20250708173752-d6b35c41f0ae5 |
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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/mattermost/mattermost-server to 10.8.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-q453-638c-h4mr 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 pinpoints whether GHSA-q453-638c-h4mr is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-q453-638c-h4mr. 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-q453-638c-h4mr in your dependencies?
O3 detects GHSA-q453-638c-h4mr across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.