GHSA-m5rv-56xx-hfc6 is a high-severity (CVSS 7.5) CWE-770 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.
Mattermost fails to properly handle very long passwords
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- 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 GHSA-m5rv-56xx-hfc6.
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
GHSA-m5rv-56xx-hfc6 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🐹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 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly handle very long passwords, which allows an attacker to overload the server CPU and memory via executing login attempts with multi-megabyte passwords. Mattermost Advisory ID: MMSA-2026-00587
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/mattermost/mattermost/server/v8 | all versions | 8.0.0-20260129164748-7201f42d955fgo get github.com/mattermost/mattermost/server/v8@v8.0.0-20260129164748-7201f42d955f |
| 🐹Go | github.com/mattermost/mattermost-server | all versions | 5.3.2-0.20260129164748-7201f42d955fgo get github.com/mattermost/mattermost-server@v5.3.2-0.20260129164748-7201f42d955f |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 10.11.0-rc1&&< 10.11.11 | 10.11.11go get github.com/mattermost/mattermost-server@v10.11.11 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 11.2.0-rc1&&< 11.2.3 | 11.2.3go get github.com/mattermost/mattermost-server@v11.2.3 |
| 🐹Go | github.com/mattermost/mattermost-server | ≥ 11.3.0-rc1&&< 11.3.1 | 11.3.1go get github.com/mattermost/mattermost-server@v11.3.1 |
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 8.0.0-20260129164748-7201f42d955f or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-m5rv-56xx-hfc6 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 GHSA-m5rv-56xx-hfc6 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-m5rv-56xx-hfc6. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-m5rv-56xx-hfc6 in your dependencies?
O3 Security finds GHSA-m5rv-56xx-hfc6 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.