CVE-2017-18915 — mattermost-server
CRITICALCVE-2017-18915 is a critical-severity (CVSS 9.8) Incorrect Default Permissions 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 server restarts may provide attackers with API access
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
CVE-2017-18915 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 377,333 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 3.8.2, 3.7.5, and 3.6.7. After a restart of a server, an attacker might suddenly gain API Endpoint access.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost-server | all versions | 3.6.7-0.20170420152529-0968e4079e0ago get github.com/mattermost/mattermost-server@v3.6.7-0.20170420152529-0968e4079e0a |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 3.7.0&&< 3.7.5 | 3.7.5go get github.com/mattermost/mattermost-server@v3.7.5 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 3.8.0&&< 3.8.2 | 3.8.2go get github.com/mattermost/mattermost-server@v3.8.2 |
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 3.6.7-0.20170420152529-0968e4079e0a or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2017-18915 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 CVE-2017-18915 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2017-18915. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2017-18915 in your dependencies?
O3 Security finds CVE-2017-18915 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.