CVE-2026-5740
Mattermost doesn't properly validate msgpack-encoded WebSocket frames before memory allocation in github.com/mattermost/mattermost-server
7.5
HIGH
CVSS 3.1
EPSS 0.33%
Description
Mattermost doesn't properly validate msgpack-encoded WebSocket frames before memory allocation in github.com/mattermost/mattermost-server
How to fix CVE-2026-5740
To remediate CVE-2026-5740, upgrade the affected package to a fixed version below.
- —upgrade to 11.6.1 or later
- —upgrade to 10.11.15+incompatible or later
- —no fix listed
- —no fix listed
- —upgrade to 8.0.0-20260410202636-17939826efa2 or later
- —upgrade to 8.0.0-20260410202636-17939826efa2 or later
Is CVE-2026-5740 being exploited?
Low — EPSS is 0.3%, meaning exploitation activity has not been observed at scale.
Affected packages (6)
- >= 11.6.0, < 11.6.1
- >= 10.11.0+incompatible, < 10.11.15+incompatible, >= 11.4.0+incompatible, < 11.4.5+incompatible, >= 11.5.0+incompatible, < 11.5.4+incompatible, >= 11.6.0+incompatible, < 11.6.1+incompatible
- from 0
- from 0
- from 0, < 8.0.0-20260410202636-17939826efa2
- from 0, < 8.0.0-20260410202636-17939826efa2
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |