Mattermost fails to properly check the authorization of POST /api/v4/teams when passing a team override scheme ID in the request, allowing an authenticated attacker with knowledge of a Team Override Scheme ID to create a new team with said team override scheme.

Mattermost fails to verify channel membership when linking a board to a channel allowing a low-privileged authenticated user to link a Board to a private channel they don't have access to, 

Mattermost fails to properly validate the origin of a websocket connection allowing a MITM attacker on Mattermost to access the websocket APIs.

Mattermost fails to properly restrict requests to localhost/intranet during the interactive dialog, which could allow an attacker to perform a limited blind SSRF.

Mattermost fails to restrict a user with permissions to edit other users and to create personal access tokens from elevating their privileges to system admin

When archiving a team, Mattermost fails to sanitize the related Websocket event sent to currently connected clients. This allows the clients to see the name, display name, description, and other data about the archived team.

Mattermost fails to redact from audit logs the user password during user creation and the user password hash in other operations if the experimental audit logging configuration was enabled (ExperimentalAuditSettings section in config).

Mattermost allows an attacker to request a preview of an existing message when creating a new message via the createPost API call, disclosing the contents of the linked message.

Boards in Mattermost allows an attacker to upload a malicious SVG image file as an attachment to a card and share it using a direct link to the file.

When running in a High Availability configuration, Mattermost fails to sanitize some of the user_updated and post_deleted events broadcast to all users, leading to disclosure of sensitive information to some of the users with currently connected Websocket clients.