CVE-2026-4274
Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access
CVSS Score
5.4
EPSS Score
0.0%
EPSS Percentile
7th
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
| CWE | CWE-863 |
| Vendor | mattermost |
| Product | mattermost |
| Published | Mar 26, 2026 |
| Last Updated | Mar 26, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None
Affected Versions
Mattermost / Mattermost
11.2.0 ≤ 11.2.2 10.11.0 ≤ 10.11.10 11.4.0 ≤ 11.4.0 11.3.0 ≤ 11.3.1
Credits
daw10