CVE-2026-4274
Medium
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
SeverityMedium
CVSS5.4
Exploit probability—
Product
Mattermost Server
PublishedMar 26, 2026
First seenMar 26, 2026
Weakness typeCWE-863Incorrect authorization
How to fix
Update
- mattermost mattermost_server10.11.11, 11.2.3, 11.3.2, 11.4.1 or later
- github.com/mattermost/mattermost/server/v811.4.1, 11.3.2, 11.2.3, 10.11.11, 8.0.0-20260217110922-b7d4a1f1f59b or later
- github.com/mattermost/mattermost-server10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatible or later
Vendor advisories
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mattermost mattermost_server | 10.11.0 ≤ v < 10.11.11, 11.2.0 ≤ v < 11.2.3, 11.3.0 ≤ v < 11.3.2, 11.4.0 ≤ v < 11.4.1 | 10.11.11, 11.2.3, 11.3.2, 11.4.1 |
| github.com/mattermost/mattermost/server/v8Go | 11.4.0-rc1 ≤ v < 11.4.1, 11.3.0-rc1 ≤ v < 11.3.2, 11.2.0-rc1 ≤ v < 11.2.3, 10.11.0-rc1 ≤ v < 10.11.11, 8.0.0-20260105080200-d27a2195068d ≤ v < 8.0.0-20260217110922-b7d4a1f1f59b | 11.4.1, 11.3.2, 11.2.3, 10.11.11, 8.0.0-20260217110922-b7d4a1f1f59b |
| github.com/mattermost/mattermost-serverGo | 10.11.0-rc1+incompatible ≤ v < 10.11.11+incompatible, 11.2.0-rc1+incompatible ≤ v < 11.2.3+incompatible, 11.3.0-rc1+incompatible ≤ v < 11.3.2+incompatible, 11.4.0-rc1+incompatible ≤ v < 11.4.1+incompatible | 10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatible |
| github.com/mattermost/mattermost-server/v5Go | No range specified | — |
| github.com/mattermost/mattermost-server/v6Go | No range specified | — |
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