CVE-2026-4274
Mattermost has an Incorrect Authorization issue
5.4
MEDIUM
CVSS 3.1
EPSS 0.04%
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
How to fix CVE-2026-4274
To remediate CVE-2026-4274, upgrade the affected package to a fixed version below.
- —upgrade to 11.4.1 or later
Is CVE-2026-4274 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- >= 11.4.0-rc1, < 11.4.1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM5.4 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N |