CVE-2026-4274CWE-863

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

Medium · published March 26, 2026

CVSS v3.1
5.4
EPSS
0%
Percentile
13.1
In the wild
Unconfirmed
What it is

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

The record
Technical detail
CVSS v3.1
5.4 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
CVSS v4.0
Not supplied
EPSS
0.00230 · 13.1th percentile
Weakness
CWE-863 · Incorrect Authorization
Published
2026-03-26T10:43Z
EPSS history
Timeline
  • 26 MAR 10:43Z
    Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access
    cvelistv5