CVE-2026-9859
MediumCVSS 6.5Exploitation Probability (EPSS)
Low risk17th percentile - higher than 17% of all known CVEs
Summary
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.
Risk Assessment
Risk of unauthorized modification of board-channel links, potentially leading to access control bypass and unauthorized data access.
Recommendation
Update Mattermost to a patched version as recommended by the vendor.
Original NVD description (English source)
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