CVE-2025-12689 DoS in Calls plugin via malformed UTF-8 in WebSocket request

What is CVE-2025-12689?

CVE-2025-12689 is a medium-severity denial of service vulnerability in Mattermost Mattermost Server, published on 17 Dec 2025. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Mattermost versions 11.0.x <= 11.0.4, 10.12.x <= 10.12.2, 10.11.x <= 10.11.6 fail to check WebSocket request field for proper UTF-8 format, which allows attacker to crash Calls plug-in via sending malformed request.

Weakness: CWE-1287

Which versions are affected by CVE-2025-12689?

3 open source packages ship an affected version, including github.com/mattermost/mattermost-plugin-calls. It affects 1 product.

Products include Mattermost Mattermost Server.

How do I fix CVE-2025-12689?

Upgrade github.com/mattermost/mattermost-plugin-calls to 1.11.0 or later.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2025-12689 being exploited?

There is no known exploitation of CVE-2025-12689 in the wild and no public exploit code.

Other vulnerabilities in Mattermost Mattermost Server

• CVE-2025-12419 Account takeover on OAuth/OpenID-enabled servers Critical 9.9
• CVE-2025-12421 Account Takeover via Code Exchange Endpoint Critical 9.9
• CVE-2025-4981 Path Traversal Leading to RCE by Any Authenticated Mattermost User Critical 9.9
• CVE-2025-20051 Arbitrary file read via block duplication in Mattermost Boards Critical 9.9
• CVE-2025-25279 Arbitrary file read in Mattermost Boards via import & export board archive Critical 9.9

All Mattermost Mattermost Server vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-j5vq-62gr-8v3r, GO-2025-4255.