CVSS 3.1
7.5 highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HCVE-2026-5740
Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users via a crafted binary WebSocket message sent to the public WebSocket endpoint.. Mattermost Advisory ID: MMSA-2026-00647
Severity
- EPSS
- 0.3% chance of exploitation in the next 30 days; higher than 27% of CVEs (scores of 2026-10-31)
- CWE
- CWE-789
- Published
- Modified
- Record from
- the NVD, synced
Affected
- mattermost:mattermost_server
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-w9m8-p4cc-4qj9 | Go | github.com/mattermost/mattermost-server | >=11.6.0 <11.6.1 | 11.6.1 |
| GHSA-w9m8-p4cc-4qj9 | Go | github.com/mattermost/mattermost-server | >=11.5.0 <11.5.4 | 11.5.4 |
| GHSA-w9m8-p4cc-4qj9 | Go | github.com/mattermost/mattermost-server | >=11.4.0 <11.4.5 | 11.4.5 |
| GHSA-w9m8-p4cc-4qj9 | Go | github.com/mattermost/mattermost-server | >=10.11.0 <10.11.15 | 10.11.15 |
| GHSA-w9m8-p4cc-4qj9 | Go | github.com/mattermost/mattermost/server/v8 | <8.0.0-20260410202636-17939826efa2 | 8.0.0-20260410202636-17939826efa2 |
| GO-2026-5838 | Go | github.com/mattermost/mattermost-server | >=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 | 10.11.15+incompatible, 11.4.5+incompatible, 11.5.4+incompatible, 11.6.1+incompatible |
| GO-2026-5838 | Go | github.com/mattermost/mattermost-server/v5 | all versions | no fix published |
| GO-2026-5838 | Go | github.com/mattermost/mattermost-server/v6 | all versions | no fix published |
| GO-2026-5838 | Go | github.com/mattermost/mattermost/server/v8 | <8.0.0-20260410202636-17939826efa2 | 8.0.0-20260410202636-17939826efa2 |