CVE-2026-9816 evidence review
Mattermost Mattermost, mattermost server
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 and POST /api/v2/teams/{teamID}/archive/import.. Mattermost Advisory ID: MMSA-2026-00685
This record remains available for product and version identification, but it is not presented as a complete remediation procedure. Confirm the affected range and the supported fix in a direct vendor advisory before changing production systems.
Identify the product and installed version
Record whether Mattermost Mattermost, mattermost server is present, where it is installed, and which interfaces are exposed.
- Record the product name, package or appliance identifier, and installed version.
- Identify internet-facing, administrative, API, and internal access paths.
- Preserve the pre-change configuration and relevant service logs.
Compare the affected range
Use the current record as an identification aid: >= 11.7.0 <= 11.7.6, >= 10.11.0 <= 10.11.21, >= 11.8.0 <= 11.8.3, >= 10.11.0 < 10.11.22, >= 11.7.0 < 11.7.7, >= 11.8.0 < 11.8.4. Resolve incomplete inventory results before deciding that an asset is unaffected.
Verify the authoritative remediation source
Open the linked source material and locate a direct vendor advisory for this CVE. Confirm the supported fixed release and product-specific update path before making a production change.
Operational boundary
This page does not replace the vendor advisory, support contract, change-management process, or recovery plan. Do not infer that an asset is unaffected from an incomplete inventory query or a missing fixed-version field.