CVE-2026-6342: Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to appropriately check for valid namespaces which allows plugin users to create subscriptions…

PriorityP423medium4.3CVSS 3.1

AVNACLPRLUINSUCNILAN

EPSS

0.15%

4.8th percentile

Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to appropriately check for valid namespaces which allows plugin users to create subscriptions to groups that were not whitelisted via creating groups that share the same prefix as a whitelisted group. Mattermost Advisory ID: MMSA-2026-00601

Affected

4 ranges

Vendor	Product	Version range	Fixed in
mattermost	mattermost	<= 11.1.5	—
mattermost	mattermost_server	10.13.0 – 10.13.11	—
mattermost	mattermost_server	11.1.0 – 11.1.5	—
mattermost	mattermost_server	11.3.0 – 11.3.4	—

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