GitHub Advisoryadvisory · Go

GHSA-w9m8-p4cc-4qj9 Mattermost doesn't properly validate msgpack-encoded WebSocket frames before memory allocation

HIGH Published 2026-05-26 Modified 2026-06-29 Official page ↗
Aliases
CVE-2026-5740
Ecosystem
Go
Packages
github.com/mattermost/mattermost-server, github.com/mattermost/mattermost/server/v8
Severity
High
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weaknesses
CWE-789
Reviewed
2026-06-29

Affected packages

• Go github.com/mattermost/mattermost-server: >= 11.6.0, < 11.6.1 → fixed in 11.6.1 • Go github.com/mattermost/mattermost-server: >= 11.5.0, < 11.5.4 → fixed in 11.5.4 • Go github.com/mattermost/mattermost-server: >= 11.4.0, < 11.4.5 → fixed in 11.4.5 • Go github.com/mattermost/mattermost-server: >= 10.11.0, < 10.11.15 → fixed in 10.11.15 • Go github.com/mattermost/mattermost/server/v8: < 8.0.0-20260410202636-17939826efa2 → fixed in 8.0.0-20260410202636-17939826efa2

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

Related

Alias · CVE (1)

  • 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… vulnerability

Weakness · CWE (1)

  • CWE-789 Memory Allocation with Excessive Size Value weakness

References