CVE-2026-9693 Mattermost thread memberships persist after team removal, exposing private channel thread metadata on re-invite
Previously removed users can view private channel thread metadata upon re-invitation due to persistent thread membership records.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-9693?
CVE-2026-9693 is a low-severity vulnerability in Mattermost Mattermost Server, published on 17 Aug 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
Mattermost versions 10.11.x <= 10.11.20, 11.7.x <= 11.7.5 Mattermost fails to remove thread membership records when a user is removed from or leaves a team, which allows a previously removed user who is later re-invited to the team to view private channel thread root post content and metadata via the team threads API.. Mattermost Advisory ID: MMSA-2026-00682
Weakness: CWE-459
Which versions are affected by CVE-2026-9693?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-9693?
Upgrade to a fixed version.
Is CVE-2026-9693 being exploited?
There is no known exploitation of CVE-2026-9693 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-f5mp-j4vf-9jp4, MINI-8r5q-gf4g-xvmw, MINI-v74c-x4cr-8xrp.