GHSA-63wg-qmrv-7q66 is a medium-severity (CVSS 5.3) 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 Server allows attackers to log sensitive information via DEBUG REST API logging endpoint
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-63wg-qmrv-7q66 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 377,166 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-serverReal-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
An issue was discovered in Mattermost Server before 4.2.0, 4.1.1, and 4.0.5. It allows attackers to add DEBUG lines to the logs via a REST API version 3 logging endpoint.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 4.1.0&&< 4.1.1 | 4.1.1go get github.com/mattermost/mattermost-server@v4.1.1 |
| 🐹Go | github.com/mattermost/mattermost-server | all versions | 4.0.5go get github.com/mattermost/mattermost-server@v4.0.5 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 4.2.0-rc1&&< 4.2.0 | 4.2.0go get github.com/mattermost/mattermost-server@v4.2.0 |
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 4.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-63wg-qmrv-7q66 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-63wg-qmrv-7q66 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-63wg-qmrv-7q66. 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-63wg-qmrv-7q66 in your dependencies?
O3 Security finds GHSA-63wg-qmrv-7q66 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.