CVE-2026-4339 SSRF via unvalidated attachment URLs in Mattermost Agents plugin MCP server

Mattermost versions 10.11.x = 10.11.18, 11.6.x = 11.6.3, 11.5.x = 11.5.6 fail to validate attachment URLs against internal or private IP ranges in the Mattermost Agents plugin MCP server which allows an attacker with access to the MCP server in stdio mode to perform server-side request forgery SS...

CVE-2026-9699 Mattermost Agents plugin logs unsanitized OpenAI API keys on authentication errors

Mattermost Plugins versions =11.6 10.18.11 11.3.6 11.6.5.0 fail to sanitize error responses from the OpenAI API before logging, which allows a user with access to server logs or support packets to obtain a valid or partially reconstructable OpenAI API key via inspection of mattermost.log entries...

CVE-2025-55074 Channel member objects leak read status

Mattermost versions 10.11.x = 10.11.3, 10.5.x = 10.5.11 fail to enforce access permissions on the Agents plugin which allows other users to determine when users had read channels via channel member objects...