CVE-2026-19603 Private channel ID disclosure via user status endpoints
Authenticated users can view private channel IDs of other users via status endpoints, exposing sensitive channel metadata.
- 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-2026-19603?
CVE-2026-19603 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 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the user status API endpoints, which allows an authenticated user to learn the channel ID of a private channel another user is actively viewing via the status endpoints, without being a member of that channel. Mattermost Advisory ID: MMSA-2026-00765
Weakness: CWE-201
Which versions are affected by CVE-2026-19603?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-19603?
No fix has been published for CVE-2026-19603 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-19603 being exploited?
There is no known exploitation of CVE-2026-19603 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-7ggq-hqj4-w5vc.