CVE-2026-5740

HIGH

Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server

Title source: cna
STIX 2.1

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

References (1)

Core 1
Core References
Vendor Advisory vendor-advisory
MMSA-2026-00647
https://mattermost.com/security-updates

Scores

CVSS v3 7.5
EPSS 0.0008
EPSS Percentile 23.6%
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CISA SSVC

Vulnrichment
Exploitation none
Automatable yes
Technical Impact partial

Details

CWE
CWE-789
Status published
Products (9)
Mattermost/Mattermost 10.11.0 - 10.11.14
Mattermost/Mattermost 10.11.15
Mattermost/Mattermost 11.4.0 - 11.4.4
Mattermost/Mattermost 11.4.5
Mattermost/Mattermost 11.5.0 - 11.5.3
Mattermost/Mattermost 11.5.4
Mattermost/Mattermost 11.6.0
Mattermost/Mattermost 11.6.1
Mattermost/Mattermost 11.7.0
Published May 22, 2026
Tracked Since May 22, 2026