CVE-2026-6342

Medium

Description

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

SeverityMedium

CVSS4.3

Exploit probability—

Product

Mattermost Server

PublishedMay 18, 2026

First seenMay 18, 2026

Weakness typeCWE-863Incorrect authorization

How to fix

Vendor advisories

mattermost.com/security-updates

Affected products

Product	Affected versions	Fixed in
mattermost mattermost_server	10.13.0 ≤ v ≤ 10.13.11, 11.1.0 ≤ v ≤ 11.1.5, 11.3.0 ≤ v ≤ 11.3.4	—

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