VULNERABILITY INTELLIGENCE

CVE-2026-5740

CVSS score7.5 HIGH
EPSS probability0.34%
CISA KEVNot currently listed
Published2026-05-22
Last modified2026-07-23
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Description

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

Weakness classification

  • responsibledisclosure@mattermost.com: CWE-789

Primary references