Mattermost MS Teams plugin doesn't limit the request body size on the /changes webhook endpoint

Denial of service in Mattermost

Mattermost Sever fails to redact the DB username and password before emitting an application log during server initialization. 

Mattermost versions 9.5.x <= 9.5.5 and 9.8.0, when using shared channels with multiple remote servers connected, fail to check that the remote server A requesting the server B to update the profile picture of a user is the remote that actually has the user as a local one . This allows a malicious remote A to change the profile images of users that belong to another remote server C that is connected to the server A.

Mattermost versions 9.5.x <= 9.5.7 and 9.10.x <= 9.10.0 fail to time limit and size limit the CA path file in the ElasticSearch configuration which allows a System Role with access to the Elasticsearch system console to add any file as a CA path field, such as /dev/zero and, after testing the connection, cause the application to crash.

Mattermost failed to disallow the modification of local users when syncing users in shared channels

Mattermost doesn't restrict which roles can promote a user as system admin

Mattermost fails to check if an admin user account active after an oauth2 flow is started, allowing an attacker with admin privileges to retain persistent access to Mattermost by obtaining an oauth2 access token while the attacker's account is deactivated.

Mattermost doesn't redact remote users' original email addresses

Mattermost fails to unescape Markdown strings in a memory-efficient way, allowing an attacker to cause a Denial of Service by sending a message containing a large number of escaped characters.

Mattermost Open Redirect vulnerability

Mattermost fails to check the Show Full Name option at the /api/v4/teams/TEAM_ID/top/team_members endpoint allowing a member to get the full name of another user even if the Show Full Name option was disabled

Mattermost Server Missing Authorization vulnerability

The Guest account feature in Mattermost version 6.7.0 and earlier fails to properly restrict the permissions, which allows a guest user to fetch a list of all public channels in the team, in spite of not being part of those channels.

Mattermost Uncontrolled Resource Consumption vulnerability

Mattermost Uncontrolled Resource Consumption vulnerability

Mattermost Mobile fails to limit the maximum number of Markdown elements in a post allowing an attacker to send a post with hundreds of emojis to a channel and freeze the mobile app of users when viewing that particular channel. 

Mattermost version 2.10.0 and earlier fails to sanitize deeplink paths, which allows an attacker to perform CSRF attacks against the server.

Mattermost Plugins versions <=2.1.3.0 fail to limit the request body size on the {{/changes}} webhook endpoint which allows an authenticated attacker to cause memory exhaustion and denial of service via sending an oversized JSON payload. Mattermost Advisory ID: MMSA-2026-00611

Mattermost versions 9.9.x <= 9.9.1, 9.5.x <= 9.5.7, 9.10.x <= 9.10.0 and 9.8.x <= 9.8.2 fail to restrict which roles can promote a user as system admin which allows a System Role with edit access to the permissions section of system console to update their role (e.g. member) to include the `manage_system` permission, effectively becoming a System Admin.