Cloudanix VulnDB

CVE-2026-9816

High · 8.3

CVSS

8.3

EPSS

0.4%

Published

Aug 17, 2026

CISA due date

—

The record

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

Affected packages

Ecosystem Package Introduced Fixed

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