CVE-2025-20051 is a critical-severity (CVSS 9.9) Path Traversal vulnerability in github.com/mattermost/mattermost/server/v8. A fix is available for github.com/mattermost/mattermost/server/v8 — see the affected versions and patch details below.
Arbitrary file read via block duplication in Mattermost Boards
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-20051.
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-2025-20051 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 378,567 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/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 10.4.x <= 10.4.1, 9.11.x <= 9.11.7, 10.3.x <= 10.3.2, 10.2.x <= 10.2.2 fail to properly validate input when patching and duplicating a board, which allows a user to read any arbitrary file on the system via duplicating a specially crafted block in Boards.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost/server/v8 | all versions | 8.0.0-20250122165010-4ed702ccff4ego get github.com/mattermost/mattermost/server/v8@v8.0.0-20250122165010-4ed702ccff4e |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | ≥ 9.11.0-rc1&&< 9.11.8 | 9.11.8go get github.com/mattermost/mattermost/server/v8@v9.11.8 |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | ≥ 10.2.0-rc1&&< 10.2.3 | 10.2.3go get github.com/mattermost/mattermost/server/v8@v10.2.3 |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | ≥ 10.3.0-rc1&&< 10.3.3 | 10.3.3go get github.com/mattermost/mattermost/server/v8@v10.3.3 |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | ≥ 10.4.0-rc1&&< 10.4.2 | 10.4.2go get github.com/mattermost/mattermost/server/v8@v10.4.2 |
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/v8, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/mattermost/mattermost/server/v8 to 8.0.0-20250122165010-4ed702ccff4e or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-20051 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-2025-20051 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-20051. 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-2025-20051 in your dependencies?
O3 Security finds CVE-2025-20051 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.