CVE-2025-9078 is a medium-severity (CVSS 4.3) CWE-328 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.
Weak cache keys lead to post IDOR and link preview poisoning
Exploitation Status
No confirmed exploitation observed yet
- 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-2025-9078.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹github.com/mattermost/mattermost-server🐹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 10.8.x <= 10.8.3, 10.5.x <= 10.5.8, 9.11.x <= 9.11.17, 10.10.x <= 10.10.1, 10.9.x <= 10.9.3 fail to properly validate cache keys for link metadata which allows authenticated users to access unauthorized posts and poison link previews via hash collision attacks on FNV-1 hashing
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.8.0&&< 10.8.4 | 10.8.4go get github.com/mattermost/mattermost-server@v10.8.4 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.5.0&&< 10.5.9 | 10.5.9go get github.com/mattermost/mattermost-server@v10.5.9 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 9.11.0&&< 9.11.18 | 9.11.18go get github.com/mattermost/mattermost-server@v9.11.18 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.10.0&&< 10.10.2 | 10.10.2go get github.com/mattermost/mattermost-server@v10.10.2 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.9.0&&< 10.9.4 | 10.9.4go get github.com/mattermost/mattermost-server@v10.9.4 |
| 🐹Go | github.com/mattermost/mattermost/server/v8 | all versions | 8.0.0-20250718075842-cd87e5c87737go get github.com/mattermost/mattermost/server/v8@v8.0.0-20250718075842-cd87e5c87737 |
Affected Products
mattermost servermattermostDetection & 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 10.8.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-9078 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.
Frequently Asked Questions
Is CVE-2025-9078 in your dependencies?
Find it across Go, including transitive dependencies.