CVE-2026-10080: Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fails to validate WebSocket command field types which allows an authenticated user…

PriorityP337medium6.5CVSS 3.1

AVNACLPRLUINSUCNINAH

EPSS

0.42%

35.2th percentile

Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fails to validate WebSocket command field types which allows an authenticated user to crash the plugin process and deny service to all Boards users via a custom_focalboard_SUBSCRIBE_TEAM message with a non-string teamId.. Mattermost Advisory ID: MMSA-2026-00687

Affected

6 ranges

Vendor	Product	Version range	Fixed in
mattermost	mattermost	10.11.0 – 10.11.21	—
mattermost	mattermost	11.7.0 – 11.7.6	—
mattermost	mattermost	11.8.0 – 11.8.3	—
mattermost	mattermost_server	>= 10.11.0 < 10.11.22	10.11.22
mattermost	mattermost_server	>= 11.7.0 < 11.7.7	11.7.7
mattermost	mattermost_server	>= 11.8.0 < 11.8.4	11.8.4

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