CVE-2026-4274

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

Published Mar 26, 2026 CVSS 3.1 · 5.4 Medium EPSS < 1% KEV · Not listed
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

Remediation

Vendor Solution

Update Mattermost to versions 11.5.0, 11.2.3, 10.11.11, 11.4.1, 11.3.2 or higher.

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-g7fp-cqj5-x8hf Mattermost has an Incorrect Authorization issue
References
History
Type Values Removed Values Added
First Time appeared Mattermost mattermost
Vendors & Products Mattermost mattermost
Type Values Removed Values Added
First Time appeared Mattermost
Mattermost mattermost Server
CPEs cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
Vendors & Products Mattermost
Mattermost mattermost Server
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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
Title Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access
Weaknesses CWE-863
References
Metrics cvssV3_1

{'score': 5.4, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
Mattermost
Published
Updated
Mar 26, 2026, 1:58 PM
Reserved
Mar 16, 2026, 3:18 PM
Status
Analyzed
Published
Mar 26, 2026, 11:16 AM
Modified
Jun 17, 2026, 10:56 AM