CVE-2025-13821
MEDIUMCVE-2025-13821 is a medium-severity (CVSS 5.7) Information Exposure vulnerability in github.com/mattermost/mattermost/server/v8. O3 Security confirms whether CVE-2025-13821 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
User profile update exposes password hash and MFA secrets
Blast Radius
github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost-server🐹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
Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to sanitize sensitive data in WebSocket messages which allows authenticated users to exfiltrate password hashes and MFA secrets via profile nickname updates or email verification events. Mattermost Advisory ID: MMSA-2025-00560
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost/server/v8 | all versions | 8.0.0-20251210191531-cd17b61de41b |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 11.1.0 | No fix |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.11.0 | No fix |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 11.2.0 | No fix |
| 🐹Go | github.com/mattermost/mattermost-server | all versions | 5.3.2-0.20251210191531-cd17b61de41b |
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/v8. 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/v8 to 8.0.0-20251210191531-cd17b61de41b or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-13821 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 CVE-2025-13821 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 CVE-2025-13821. 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-2025-13821 in your dependencies?
O3 detects CVE-2025-13821 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.