CVE-2026-4274

MEDIUM

Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access

Title source: cna

Description

Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel via sending crafted membership sync messages that trigger team membership assignment. Mattermost Advisory ID: MMSA-2026-00574

References (1)

[Vendor Advisory] https://mattermost.com/security-updates

Scores

CVSS v3 5.4

EPSS 0.0003

EPSS Percentile 8.5%

Attack Vector NETWORK

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

Details

CWE

CWE-863

Status published

Products (11)

Mattermost/Mattermost 10.11.0 - 10.11.10

Mattermost/Mattermost 10.11.11

Mattermost/Mattermost 11.2.0 - 11.2.2

Mattermost/Mattermost 11.2.3

Mattermost/Mattermost 11.3.0 - 11.3.1

Mattermost/Mattermost 11.3.2

Mattermost/Mattermost 11.4.0

mattermost/mattermost 11.4.0-rc1 - 11.4.1Go

Mattermost/Mattermost 11.4.1

Mattermost/Mattermost 11.5.0

... and 1 more

Published Mar 26, 2026

Tracked Since Mar 26, 2026