Inconsistent state in UI after boards permission change by system admin

Mattermost fails to properly show information in the UI, allowing a system admin to modify a board state allowing any user with a valid sharing link to join the board with editor access, without the UI showing the updated permissions.

Disabling publicly-shared boards does not disable existing publicly available board links

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.

channel DoS by sharing a boards link

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

Member can create team with team override scheme

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.

Lack of channel membership check when linking a board to a channel

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, 

WebSockets accept connections from HTTPS origin

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

Limited blind SSRF to localhost/intranet in interactive dialog implementation

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 6.0 and earlier fails to sufficiently validate parameters during post creation, which allows authenticated attackers to cause a client-side crash of the web application via a maliciously crafted post.

Mattermost 6.0 and earlier fails to sufficiently validate the email address during registration, which allows attackers to trick users into signing up using attacker-controlled email addresses via crafted invitation token.

An issue was discovered in Mattermost Server before 5.19.0, 5.18.1, 5.17.3, 5.16.5, and 5.9.8. Creation of a trusted OAuth application does not always require admin privileges, aka MMSA-2020-0001.

An issue was discovered in Mattermost Server before 5.19.0. Attackers can rename a channel and cause a collision with a direct message, aka MMSA-2020-0002.

An issue was discovered in Mattermost Server before 5.19.0. Attackers can discover private channels via the "get channel by name" API, aka MMSA-2020-0004.

An issue was discovered in Mattermost Server before 5.20.0. Non-members can receive broadcasted team details via the update_team WebSocket event, aka MMSA-2020-0012.

An issue was discovered in Mattermost Server before 5.21.0. Socket read operations are not appropriately restricted, which allows attackers to cause a denial of service, aka MMSA-2020-0005.

An issue was discovered in Mattermost Server before 5.21.0. mmctl allows directory traversal via HTTP, aka MMSA-2020-0014.

An issue was discovered in Mattermost Server before 5.22.0. The markdown renderer allows attackers to cause a denial of service (client-side), aka MMSA-2020-0017.

An issue was discovered in Mattermost Server before 5.23.0. Automatic direct message replies allow attackers to cause a denial of service (infinite loop), aka MMSA-2020-0020.

An issue was discovered in Mattermost Server before 5.23.0. Large webhook requests allow attackers to cause a denial of service (infinite loop), aka MMSA-2020-0021.

An issue was discovered in Mattermost Server before 5.7. It allows a bypass of e-mail address discovery restrictions.

An issue was discovered in Mattermost Server before 5.7, 5.6.3, 5.5.2, and 4.10.5. It mishandles permissions for user-access token creation.