CVE-2026-6517 Mattermost Desktop App fails to restrict the allow list of domains which NTLM credentials are passed

Mattermost Desktop App versions =6.1 5.5.13.0 fail to restrict the allow list of domains to which NTLM credentials were forwarded to in the Mattermost Desktop App which allows any user on a server without the image proxy enabled to intercept other users credentials via embedding an image that...

PT-2026-49238

Name of the Vulnerable Software and Affected Versions Mattermost Desktop App versions prior to 6.1 Mattermost Desktop App version 5.5.13.0 Description The application fails to restrict the allow list of domains for NTLM credential forwarding. This allows a user on a server where the image proxy i...

CVE-2026-3433

Mattermost versions 11.6.x = 11.6.1, 11.5.x = 11.5.4, 10.11.x = 10.11.15, 10.11.x = 10.11.16 fail to restrict roleupdated websocket event broadcasts to members of the affected team or channel which allows an authenticated attacker with guest-level access to observe permission scheme change...

EUVD-2026-36501

Mattermost versions 11.6.x = 11.6.1, 11.5.x = 11.5.4, 10.11.x = 10.11.15, 10.11.x = 10.11.16 Fail to enforce PermissionInviteUser when setting AllowOpenInvite or AllowedDomains during team creation the check was only applied on update/patch, which allows an authenticated user holding...

CVE-2026-3117

Mattermost Plugins versions =11.5 11.1.5 10.13.11 11.3.4.0 fail to properly check for permissions when processing commands in the Gitlab plugin which allows normal users to uninstall instances or setup webhook connections via the gitlab instance option or the /gitlab webhook option commands...

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 to groups that were not whitelisted via creating groups that share the same prefix as a whitelisted group. Mattermost Advisory ID:...

CVE-2026-28735

Mattermost versions 11.6.x = 11.6.0, 11.5.x = 11.5.3, 11.4.x = 11.4.4, 10.11.x = 10.11.14 fail to validate the OAuth token scope on the callback which allows an authenticated Mattermost user to gain access to private repositories via modifying the scope parameter in the GitHub authorization URL...

EUVD-2026-31646

Mattermost versions 11.6.x = 11.6.0, 11.5.x = 11.5.3, 11.4.x = 11.4.4, 10.11.x = 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service server process termination via a crafted webhook...

CVE-2026-3473

Mattermost versions 11.6.x = 11.6.0, 11.5.x = 11.5.3, 11.4.x = 11.4.4, 10.11.x = 10.11.14 fail to validate file ownership and access control, which allows an authenticated user to access and download files belonging to other users or teams via crafted Boards API requests using valid file IDs...

CVE-2026-4635 Persistent notification timing attack causing server denial of service

Mattermost versions 11.6.x = 11.6.0, 11.5.x = 11.5.3, 11.4.x = 11.4.4, 10.11.x = 10.11.14 fail to archive the channel before removing persistent notifications which allows authenticated user to crash the server via timing the creation of persistent notification message between the server deleting...

CVE-2026-4635

Mattermost (versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x

PT-2026-42747

Name of the Vulnerable Software and Affected Versions Mattermost version 11.6.0 Mattermost version 11.5.3 Mattermost version 11.4.4 Mattermost version 10.11.14 Description An issue exists where the system fails to archive the channel before removing persistent notifications. This allows an...

CVE-2026-4858

Mattermost versions 11.6.x = 11.6.0, 11.5.x = 11.5.3, 11.4.x = 11.4.4, 10.11.x = 10.11.14 fail to check integration URL for path traversal which allows an malicious authenticated user to call an arbitrary API via system admin Mattermost auth token using via path traversal in integration action...

PT-2026-42404

Name of the Vulnerable Software and Affected Versions Mattermost version 11.5.1 Description An issue exists where the system fails to validate the team-level run create permission against the target team during the creation of a playbook run. This allows an authenticated team member to create run...

GHSA-GVG4-JHMR-6J23 Mattermost doesn't check if {{team_id}} was being changed when updating playbooks

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail to check if teamid was being changed when updating playbooks, allowing users with only Manage Playbook Configurations permission to change a playbook's team, bypassing manage members restriction via PUT api. Mattermost Advisory ID:...

Mattermost doesn't check if {{team_id}} was being changed when updating playbooks

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail to check if teamid was being changed when updating playbooks, allowing users with only Manage Playbook Configurations permission to change a playbook's team, bypassing manage members restriction via PUT api. Mattermost Advisory ID:...

GHSA-JP3F-X449-4Q75 Mattermost doesn't enforce client identity binding during the OAuth authorization code redemption flow

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail to enforce client identity binding during the OAuth authorization code redemption flow which allows an authenticated OAuth client to redeem authorization codes issued to a different client via a crafted token exchange request.. Mattermo...

Mattermost doesn't enforce client identity binding during the OAuth authorization code redemption flow

Mattermost versions 11.5.x = 11.5.1, 10.11.x = 10.11.13 fail to enforce client identity binding during the OAuth authorization code redemption flow which allows an authenticated OAuth client to redeem authorization codes issued to a different client via a crafted token exchange request.. Mattermo...

Mattermost does not verify remote cluster channel access when processing shared channel membership removals

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,...

CVE-2026-6343

Mattermost 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.. Mattermost Advisory ID: MMSA-2026-00591...