CVE-2026-28759Medium· 4.3▾ SunlitMattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows …
▾ Sunlit zone — Low / medium · no exploitation signal
impact 23.7 · likelihood 0.1 · exploitation 0
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Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
Last analysed / modified upstream
0.3%
Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any channel, including private channels, via crafted membership sync messages targeting channels the remote cluster is not authorized to access. Mattermost Advisory ID: MMSA-2026-00576
mattermost_server >= 10.11.0, < 10.11.14mattermost_server >= 11.4.0, < 11.4.4mattermost_server >= 11.5.0, < 11.5.2Upgrade past the affected range:
mattermost_server 11.5.2Connected by shared product, vendor, weakness, or advisory.
CVE-2026-6343Medium· 4.3Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to check public/private permissions which allows members without these permissions to access public playbooks via /get.
CVE-2026-4286Low· 3.1Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to check if {{team_id}} was being changed when updating playbooks, allowing users with only {{Manage Playbook Configurations}} permission to change a playbook's team, bypassi…
CVE-2026-6342Medium· 4.3Mattermost 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 pr…
CVE-2026-28732Medium· 4.3Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 Fail to enforce slash command trigger-word uniqueness during command updates which allows an authenticated team member with Manage Own Slash Commands permission …
CVE-2026-6341Medium· 4.3Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to have API-level checks on which groups the user can create issues or attach comments to which allows a user that is member of multiple groups to create issues to a locked…
CVE-2026-4273Low· 3.7Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13 fail to validate that the RefreshedToken differs from the original invite token during remote cluster invite confirmation which allows an authenticated attacker to bypass token ro…