CVE-2026-4274 MEDIUM

CVE-2026-4274: Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access

Vendor Mattermost
Product Mattermost
Weakness CWE-863 · Incorrect authorization
Published March 26, 2026
Last update March 26, 2026
View on NVD All CVEs

CVSS base score

5.4/10
Attack vector Network
Attack complexity Low
Privileges required Low
User interaction None
Confidentiality Low
Integrity Low

CVSS vector

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

What the vulnerability does

01Description

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

Key dates

02Disclosure timeline

March 26, 2026 CVE published
March 26, 2026 Record updated