CVE-2026-10085 Ordinary group/direct message member can enable group_constrained and remove all channel participants
An ordinary member can remove all participants from a conversation by improperly setting the group_constrained flag, disrupting communication.
- 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-2026-10085?
CVE-2026-10085 is a medium-severity missing authorization vulnerability in Mattermost Mattermost Server, published on 13 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to restrict the group_constrained channel flag to public and private channels that support group synchronization, which allows an ordinary group or direct message member to remove all participants from the conversation via the channel patch API.. Mattermost Advisory ID: MMSA-2026-00688
Weakness: CWE-862
Which versions are affected by CVE-2026-10085?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-10085?
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-2026-10085 being exploited?
There is no known exploitation of CVE-2026-10085 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-6v2h-jj3h-8gmx, MINI-v7xq-33ww-pgmq, MINI-x72m-qxvh-4x4q.