CVE-2026-5740HIGHCVSS 7.5

Mattermost doesn't properly validate msgpack-encoded WebSocket frames before memory allocation

Published May 26, 2026·Updated Jun 29, 2026

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

Affected Packages (2)

github.com/mattermost/mattermost/server/v8GO
Fixed in 8.0.0-20260410202636-17939826efa2
github.com/mattermost/mattermost-serverGO
Fixed in 11.6.1

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

View on NVD Search GitHub Search Google

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