Vulnerability Details CVE-2026-4274
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
Exploit prediction scoring system (EPSS) score
EPSS Score 0.0
EPSS Ranking 6.9%
CVSS Severity
CVSS v3 Score 5.4
References
Products affected by CVE-2026-4274
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cpe:2.3:a:mattermost:mattermost_server:10.11.0
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cpe:2.3:a:mattermost:mattermost_server:10.11.1
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cpe:2.3:a:mattermost:mattermost_server:10.11.10
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cpe:2.3:a:mattermost:mattermost_server:10.11.2
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cpe:2.3:a:mattermost:mattermost_server:10.11.3
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cpe:2.3:a:mattermost:mattermost_server:10.11.4
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cpe:2.3:a:mattermost:mattermost_server:10.11.5
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cpe:2.3:a:mattermost:mattermost_server:10.11.6
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cpe:2.3:a:mattermost:mattermost_server:10.11.7
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cpe:2.3:a:mattermost:mattermost_server:10.11.8
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cpe:2.3:a:mattermost:mattermost_server:10.11.9
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cpe:2.3:a:mattermost:mattermost_server:11.2.0
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cpe:2.3:a:mattermost:mattermost_server:11.2.1
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cpe:2.3:a:mattermost:mattermost_server:11.2.2
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cpe:2.3:a:mattermost:mattermost_server:11.3.0
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cpe:2.3:a:mattermost:mattermost_server:11.3.1
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cpe:2.3:a:mattermost:mattermost_server:11.4.0