CVE-2026-19541 Outgoing OAuth connection client secret exposure during connection validation
Authenticated users with management permissions can expose OAuth client secrets by manipulating token URL validation endpoints.
- 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-2026-19541?
CVE-2026-19541 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 require re-entry of the stored client secret when validating an outgoing OAuth connection, which allows an authenticated user with permission to manage outgoing OAuth connections to obtain the secret via pointing the token URL at an attacker-controlled endpoint and triggering validation.. Mattermost Advisory ID: MMSA-2026-00761
Weakness: CWE-201
Which versions are affected by CVE-2026-19541?
It affects 1 product.
Products include Mattermost Mattermost Server.
How do I fix CVE-2026-19541?
No fix has been published for CVE-2026-19541 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-19541 being exploited?
There is no known exploitation of CVE-2026-19541 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-7v3h-fv85-64q9.