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CVE-2026-9816 is an improper authorization vulnerability in Mattermost Boards. Affected Mattermost versions fail to validate BoardMember.Scheme* fields on the server side during board member insertion and team archive import processing. Because authorization-relevant fields are not properly enforced on these paths, a board editor or a non-guest team member can submit crafted requests that assign board administrator privileges to arbitrary users. The issue is exposed through the boards member creation API and the team archive import path. Affected versions include 10.11.x through 10.11.21, 11.7.x through 11.7.6, and 11.8.x through 11.8.3.
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No public exploit code observed for this vulnerability.
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8 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A specific vulnerability affecting Mattermost versions prior to or equal to 10.11.21, 11.7.6, and 11.8.3.
A specific vulnerability affecting Mattermost versions prior to or equal to 10.11.21, 11.7.6, and 11.8.3.
An improper authorization vulnerability in Mattermost that fails to validate BoardMember.Scheme* fields server-side, allowing a board editor or non-guest team member to grant board admin privileges to arbitrary users.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.