CVE-2026-10080: Boards plugin panics on WebSocket command with non-string field types

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-17 · updated 2026-08-18
Weakness: CWE-704

Description

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 products

Mattermost: from 10.11.0 before 10.11.22; from 11.7.0 before 11.7.7; from 11.8.0 before 11.8.4 — fixed in 10.11.22, 11.7.7, 11.8.4

How to fix

Upgrade to a fixed version: Mattermost 10.11.22, 11.7.7, 11.8.4. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

Get alerted when CVE-2026-10080 or the next vulnerability affects your stack