CVE-2026-18256 Private team metadata disclosure via the team search API
An authenticated user can disclose private team metadata via the search API, exposing sensitive team information to unauthorized users.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-18256?
CVE-2026-18256 is a medium-severity vulnerability in Mattermost Mattermost Server, published on 16 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to properly restrict private teams from public team search results, which allows an authenticated user without permission to list private teams to disclose the ID, name, and display name of private teams via a modified team search request. Mattermost Advisory ID: MMSA-2026-00748
Weakness: CWE-863
Which versions are affected by CVE-2026-18256?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-18256?
No fix has been published for CVE-2026-18256 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-18256 being exploited?
There is no known exploitation of CVE-2026-18256 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-mqc4-5px9-95jm.