CVE-2026-10527 Boards plugin retains Board Admin rights for users demoted to System Guest
Demoted System Guests retain Board Admin privileges, allowing unauthorized admin operations via the Boards API or UI.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-10527?
CVE-2026-10527 is a medium-severity missing authorization vulnerability in Mattermost Mattermost Server, published on 17 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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 Advisory ID: MMSA-2026-00691
Weakness: CWE-863
Which versions are affected by CVE-2026-10527?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-10527?
Apply the vendor's patch.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-10527 being exploited?
There is no known exploitation of CVE-2026-10527 in the wild and no public exploit code.
Other vulnerabilities in Mattermost Mattermost Server
- CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers
- CVE-2025-12421 Account Takeover via Code Exchange Endpoint
- CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User
- CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards
- CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive
Sources
Also known as GHSA-ghq9-4rcg-jvc2, MINI-3v4m-7h72-xjx5, MINI-6545-8wrv-38fp.