Vulnerability Details CVE-2026-9859
Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to enforce PermissionManageBoardRoles on the channelId field of the batch endpoint, which allows an authenticated board editor to relink any board they can edit to an arbitrary channel via a crafted PATCH request. Mattermost Advisory ID: MMSA-2026-00686
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 17.0%
CVSS Severity
CVSS v3 Score 6.5
References
Products affected by CVE-2026-9859
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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:10.11.11
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cpe:2.3:a:mattermost:mattermost_server:10.11.12
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cpe:2.3:a:mattermost:mattermost_server:10.11.13
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cpe:2.3:a:mattermost:mattermost_server:10.11.14
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cpe:2.3:a:mattermost:mattermost_server:10.11.15
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cpe:2.3:a:mattermost:mattermost_server:10.11.16
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cpe:2.3:a:mattermost:mattermost_server:10.11.17
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cpe:2.3:a:mattermost:mattermost_server:10.11.18
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cpe:2.3:a:mattermost:mattermost_server:10.11.19
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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:10.11.20
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cpe:2.3:a:mattermost:mattermost_server:10.11.21
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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:11.7.0
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cpe:2.3:a:mattermost:mattermost_server:11.7.1
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cpe:2.3:a:mattermost:mattermost_server:11.7.2
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cpe:2.3:a:mattermost:mattermost_server:11.7.3
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cpe:2.3:a:mattermost:mattermost_server:11.7.4
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cpe:2.3:a:mattermost:mattermost_server:11.7.5
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cpe:2.3:a:mattermost:mattermost_server:11.7.6