Mattermost Plugin Security Issues

Mattermost Plugins versions 11.4 and earlier fail to validate incoming request sizes on webhook endpoints, allowing authenticated attackers to trigger denial of service by sending oversized requests. The vulnerability affects multiple Mattermost release branches (10.x, 11.0.x, 11.1.x, 11.3.x) and has been assigned CVSS 4.9 (medium severity) with no public exploit identified at time of analysis. While exploitability requires high-privilege authentication and manual intervention, the lack of request size enforcement on webhooks represents a fundamental input validation gap that could disrupt service availability in production environments.

Mattermost Plugins versions 11.4 and earlier, including 10.11.11.0, fail to validate webhook request timestamps, enabling attackers with high privileges to replay webhook requests and corrupt Zoom meeting state within Mattermost deployments. The vulnerability carries a CVSS score of 2.2 with low attack complexity but requires high-privilege authentication; no public exploit has been identified at time of analysis, and CISA has not flagged this for active exploitation.