Mattermost ≫ Mattermost Server

Mattermost fails to restrict which parameters' values it takes from the request during signup allowing an attacker to register users as inactive, thus blocking them from later accessing Mattermost without the system admin activating their accounts.

Mattermost fails to properly validate markdown, allowing an attacker to crash the server via a specially crafted markdown input.

Mattermost WelcomeBot plugin fails to to validate the membership status when inviting or adding users to channels allowing guest accounts to be added or invited to channels by default.

Mattermost fails to properly validate a gif image file, allowing an attacker to consume a significant amount of server resources, making the server unresponsive for an extended period of time by linking to specially crafted image file.

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

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 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 overr...

Mattermost Boards fail to properly validate a board link, allowing an attacker to crash a channel by posting a specially crafted boards link.

Mattermost fails to disable public Boards after the "Enable Publicly-Shared Boards" configuration option is disabled, resulting in previously-shared public Boards to remain accessible.