What is CVE-2026-5740?

CVE-2026-5740 is a high-severity vulnerability in Mattermost, classified under CWE-789. CVSS score: 7.5/10. Published 2026-05-22.

How severe is CVE-2026-5740?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Mattermost

CVE-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…

EPSS: 0.001 (28.2th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

Mattermost — versions 11.6.0, 11.5.0, 11.4.0
Mattermost Mattermost_server

Weakness classification (CWE)

CWE-789

References

responsibledisclosure@mattermost.com (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-5740?: CVE-2026-5740 is a high-severity vulnerability in Mattermost, classified under CWE-789. CVSS score: 7.5/10. Published 2026-05-22.
How severe is CVE-2026-5740?: High severity. CVSS v3 base score is 7.5 out of 10.