CVE-2026-9693 Mattermost thread memberships persist after team removal, exposing private channel thread metadata on re-invite

Mattermost versions 10.11.x = 10.11.20, 11.7.x = 11.7.5 Mattermost fails to remove thread membership records when a user is removed from or leaves a team, which allows a previously removed user who is later re-invited to the team to view private channel thread root post content and metadata via t...

CVE-2026-9859 Mattermost Boards plugin didn’t enforce role-based authorization on board channel link allowing board editors to expose boards to arbitrary channels

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...

CVE-2026-9859 Mattermost Boards plugin didn’t enforce role-based authorization on board channel link allowing board editors to expose boards to arbitrary channels

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...

CVE-2026-9859

Mattermost Boards plugin (versions ≤11.7.6, ≤10.11.21, ≤11.8.3) fails to enforce PermissionManageBoardRoles on the batch endpoint's channelId field, allowing authenticated board editors to relink boards to arbitrary channels via crafted PATCH requests. CVSS 3.1 scores 6.5 (MEDIUM) for network-bas...

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...

CVE-2026-9816 Insufficient server-side validation of board member role fields permits privilege escalation

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21, 11.8.x = 11.8.3 fail to validate BoardMember.Scheme fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST /api/v2/boards/boardID/members a...

CVE-2026-9816

Mattermost 11.7.x (≤11.7.6), 10.11.x (≤10.11.21), and 11.8.x (≤11.8.3) lack server-side validation of BoardMember.Scheme* fields on insert and archive-import paths, allowing board editors or non-guest team members to grant Board Admin to arbitrary users via POST /api/v2/boards/{boardID}/members a...

CVE-2026-9816

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21, 11.8.x = 11.8.3 fail to validate BoardMember.Scheme fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST /api/v2/boards/boardID/members a...

CVE-2026-10080 Boards plugin panics on WebSocket command with non-string field types

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21, 11.8.x = 11.8.3 fails to validate WebSocket command field types which allows an authenticated user to crash the plugin process and deny service to all Boards users via a customfocalboardSUBSCRIBETEAM message with a non-string teamId...

CVE-2026-10080

Mattermost Boards plugin panics on WebSocket custom_focalboard_SUBSCRIBE_TEAM messages with a non-string teamId, crashing the plugin and denying service to all Boards users. Affected: 11.7.x ≤ 11.7.6, 10.11.x ≤ 10.11.21, 11.8.x ≤ 11.8.3 (MMSA-2026-00687). No in-the-wild exploitation reported. Pat...

CVE-2026-16046

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21 fail to enforce run-state validation on write operations for finished playbook runs which allows a run participant to modify status, checklists, retrospective content, ownership, and participants on completed runs via REST and GraphQL API...

CVE-2026-16048

Mattermost versions 11.8.x = 11.8.2, 11.7.x = 11.7.6, 10.11.x = 10.11.21 fail to restrict channel member role assignment to channel-scoped roles which allows a channel administrator to gain additional channel permissions via the channel member roles API.. Mattermost Advisory ID: MMSA-2026-00697...

CVE-2026-16049

Mattermost Plugins versions =11.8 10.20.11 11.5.7.0 The Mattermost GitLab plugin fails to verify channel permissions when processing API requests with a caller-supplied postid, and fails to validate the weburl parameter against the configured GitLab instance, which allows an authenticated attacke...

CVE-2026-16047

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21, 11.8.x = 11.8.3 fail to validate that users have read access to a channel before linking a board to it, which allows an authenticated attacker to discover the membership of private channels on the same team via creating, patching, importing...

CVE-2026-15754

Mattermost versions 11.7.x = 11.7.6, 11.8.x = 11.8.3 The access control policy unassign endpoint fails to re-validate that each target channel still belongs to the requesting admin's team, which allows an authenticated team administrator to remove ABAC attribute-based access control policy...

CVE-2026-10527

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21, 11.8.x = 11.8.3 fails to reconcile SchemeAdmin flags with a user's current role which allows a user demoted to System Guest to retain Board Admin privileges and perform admin-only operations via the Boards REST API or UI.. Mattermost Adviso...

CVE-2026-16045

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21 Mattermost failed to restrict OAuth deauthorization and personal access token management endpoints to direct user sessions, which allowed an OAuth app with a delegated user token to revoke the user's authorizations or tokens for other...

CVE-2026-16044

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21 fail to prevent guest users from receiving Board Admin privileges during board archive import which allows a board member to escalate a guest user to Board Admin via importing a crafted .boardarchive file. Mattermost Advisory ID:...

CVE-2026-10527

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21, 11.8.x = 11.8.3 fails to reconcile SchemeAdmin flags with a user's current role which allows a user demoted to System Guest to retain Board Admin privileges and perform admin-only operations via the Boards REST API or UI.. Mattermost Adviso...

EUVD-2026-60192

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21, 11.8.x = 11.8.3 fails to reconcile SchemeAdmin flags with a user's current role which allows a user demoted to System Guest to retain Board Admin privileges and perform admin-only operations via the Boards REST API or UI.. Mattermost Adviso...