CVE-2026-10080 Boards plugin panics on WebSocket command with non-string field types
An authenticated user can crash the Mattermost Boards plugin by sending a WebSocket message with invalid field types, denying service to all users.
- 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-2026-10080?
CVE-2026-10080 is a medium-severity denial of service 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 validate WebSocket command field types which allows an authenticated user to crash the plugin process and deny service to all Boards users via a custom_focalboard_SUBSCRIBE_TEAM message with a non-string teamId.. Mattermost Advisory ID: MMSA-2026-00687
Weakness: CWE-704
Which versions are affected by CVE-2026-10080?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-10080?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-10080 being exploited?
There is no known exploitation of CVE-2026-10080 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-523x-7gmh-rhpc, MINI-2jr5-c585-6j4q, MINI-p62f-rcj7-7xxw.