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.
https://mattermost.com/security-updates
https://euvd.enisa.europa.eu/vulnerability/EUVD-2025-203918
Source: Mitre, NVD
Published: 2025-12-17
Updated: 2026-10-13
Base Score: 6.8
Vector: CVSS2#AV:N/AC:L/Au:S/C:N/I:N/A:C
Severity: Medium
Base Score: 6.5
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS: 0.00288