CVE-2026-9859

Name of the Vulnerable Software and Affected Versions Mattermost versions 11.7.0 through 11.7.6 Mattermost versions 10.11.0 through 10.11.21 Mattermost versions 11.8.0 through 11.8.3

Description The Boards plugin fails to enforce the PermissionManageBoardRoles authorization on the channelId field of the batch endpoint. This allows an authenticated user with board editor privileges to relink any board they have permission to edit to an arbitrary channel by sending a crafted PATCH request.

Recommendations Update Mattermost versions 11.7.0 through 11.7.6 to a version newer than 11.7.6. Update Mattermost versions 10.11.0 through 10.11.21 to a version newer than 10.11.21. Update Mattermost versions 11.8.0 through 11.8.3 to a version newer than 11.8.3.