CVE-2026-3114
MEDIUMCVE-2026-3114 is a medium-severity (CVSS 6.5) CWE-409 vulnerability in github.com/mattermost/mattermost/server/v8. O3 Security confirms whether CVE-2026-3114 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Zip Bomb Denial of Service via Unrestricted Archive Decompression
Blast Radius
github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost/server/v8🐹github.com/mattermost/mattermost/server/v8Real-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 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to validate decompressed archive entry sizes during file extraction which allows authenticated users with file upload permissions to cause a denial of service via crafted zip archives containing highly compressed entries (zip bombs) that exhaust server memory.. Mattermost Advisory ID: MMSA-2026-00598
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost/server/v8 | ≥ 11.4.0&&< 11.4.1 | 11.4.1 |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | ≥ 11.3.0&&< 11.3.2 | 11.3.2 |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | ≥ 11.2.0&&< 11.2.4 | 11.2.4 |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | ≥ 10.11.0&&< 10.11.12 | 10.11.12 |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | ≥ 8.0.0-20260105080200-d27a2195068d&&< 8.0.0-20260217110922-b7d4a1f1f59b | 8.0.0-20260217110922-b7d4a1f1f59b |
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 11.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-3114 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-2026-3114 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-2026-3114. 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-2026-3114 in your dependencies?
O3 detects CVE-2026-3114 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.