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.

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.

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.

An issue was discovered in Mattermost Server before 3.0.0. It potentially allows attackers to obtain sensitive information (credential fields within config.json) via the System Console UI.

An issue was discovered in Mattermost Server before 3.0.0. It offers superfluous APIs for a Team Administrator to view account details.

Mattermost fails to properly authorize the requests fetching team associated AD/LDAP groups, allowing a user to fetch details of AD/LDAP groups of a team that they are not a member of. 

An issue was discovered in Mattermost Server before 4.8.1, 4.7.4, and 4.6.3. WebSocket events were accidentally sent during certain user-management operations, violating user privacy.

A race condition in Mattermost versions 8.1.x before 8.1.9, and 9.4.x before 9.4.2 allows an authenticated attacker to gain unauthorized access to individual posts' contents via carefully timed post creation while another user deletes posts.

An issue was discovered in Mattermost Server before 2.2.0. It allows unintended access to information stored by a web browser.

Mattermost versions 10.4.x <= 10.4.1, 9.11.x <= 9.11.7, 10.3.x <= 10.3.2, 10.2.x <= 10.2.2 fail to properly validate input when patching and duplicating a board, which allows a user to read any arbitrary file on the system via duplicating a specially crafted block in Boards.

Mattermost Mobile Apps versions <=2.18.0 fail to disable autocomplete during login while typing the password and visible password is selected, which allows the password to get saved in the dictionary when the user has Swiftkey as the default keyboard, the masking is off and the password contains a special character..

Mattermost fails to check channel membership when accessing message threads, allowing an attacker to access arbitrary posts by using the message threads API.

Mattermost fails to sanitize code permalinks, allowing an attacker to preview code from private repositories by posting a specially crafted permalink on a channel.

A missing permissions check in the /plugins/playbooks/api/v0/runs API in Mattermost allows an attacker to list and view playbooks belonging to a team they are not a member of.

Mattermost fails to perform authorization checks in the /plugins/playbooks/api/v0/runs/add-to-timeline-dialog endpoint of the Playbooks plugin allowing an attacker to get limited information about a post if they know the post ID

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2 when local storage for files is used. A System Admin can test for the existence of an arbitrary file.

One of the API in Mattermost version 6.4.1 and earlier fails to properly protect the permissions, which allows the authenticated members with restricted custom admin role to bypass the restrictions and view the server logs and server config.json file contents.

Unrestricted information disclosure of all users in Mattermost version 6.7.0 and earlier allows team members to access some sensitive information by directly accessing the APIs.

Mattermost 6.3.0 and earlier fails to protect email addresses of the creator of the team via one of the APIs, which allows authenticated team members to access this information resulting in sensitive & private information disclosure.

Mattermost fails to sanitize ephemeral error messages, allowing an attacker to obtain arbitrary message contents by a specially crafted /groupmsg command.

An issue was discovered in Mattermost Server before 5.9.0, 5.8.1, 5.7.3, and 4.10.8. It allows attackers to obtain sensitive information during user activation/deactivation.

An issue was discovered in Mattermost Server before 5.9.0, 5.8.1, 5.7.3, and 4.10.8. Changes, within the application, to e-mail addresses are mishandled.

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

Mattermost Boards plugin v0.10.0 and earlier fails to protect email addresses of all users via one of the Boards APIs, which allows authenticated and unauthorized users to access this information resulting in sensitive & private information disclosure.

An issue was discovered in Mattermost Server before 5.7.1, 5.6.4, 5.5.3, and 4.10.6. It does not honor flags API permissions when deciding whether a user can receive intra-team posts.

Mattermost fails to check the required permissions in the POST /api/v4/channels/stats/member_count API resulting in channel member counts being leaked to a user without permissions.

Mattermost versions 8.1.x before 8.1.11, 9.3.x before 9.3.3, 9.4.x before 9.4.4, and 9.5.x before 9.5.2 fail to authenticate the source of certain types of post actions, allowing an authenticated attacker to create posts as other users via a crafted post action.

Mattermost Jira Plugin handling subscriptions fails to check the security level of an incoming issue or limit it based on the user who created the subscription resulting in registered users on Jira being able to create webhooks that give them access to all Jira issues.

Mattermost fails to properly restrict the access of files attached to posts in an archived channel, resulting in members being able to access files of archived channels even if the “Allow users to view archived channels” option is disabled.

Improper Access Control in Mattermost Server versions 8.1.x before 8.1.11 allows an attacker that is in a channel with an active call to keep participating in the call even if they are removed from the channel

Mattermost fails to check the "invite_guest" permission when inviting guests of other teams to a team, allowing a member with permissions to add other members but not to add guests to add a guest to a team as long as the guest was already a guest in another team of the server

Mattermost versions 8.1.x before 8.1.9, 9.2.x before 9.2.5, and 9.3.0 fail to sanitize the metadata on posts containing permalinks under specific conditions, which allows an authenticated attacker to access the contents of individual posts in channels they are not a member of.

Mattermost fails to check if compliance export is enabled when fetching posts of public channels allowing a user that is not a member of the public channel to fetch the posts, which will not be audited in the compliance export. 

Mattermost versions 10.5.x <= 10.5.5, 9.11.x <= 9.11.15, 10.8.x <= 10.8.0, 10.7.x <= 10.7.2, 10.6.x <= 10.6.5 fail to properly validate channel membership when retrieving playbook run metadata, allowing authenticated users who are playbook members but not channel members to access sensitive information about linked private channels including channel name, display name, and participant count through the run metadata API endpoint.

Mattermost fails to perform proper authorization in the /plugins/focalboard/api/v2/users endpoint allowing an attacker who is a guest user and knows the ID of another user to get their information (e.g. name, surname, nickname) via Mattermost Boards.

Mattermost fails to validate team membership when a user attempts to access a playbook, allowing a user with permissions to a playbook but no permissions to the team the playbook is on to access and modify the playbook. This can happen if the user was once a member of the team, got permissions to the playbook and was then removed from the team. 

Mattermost fails to properly validate permissions when demoting and deactivating a user allowing for a system/user manager to demote / deactivate another manager

Mattermost fails to properly check permissions when retrieving a post allowing for a System Role with the permission to manage channels to read the posts of a DM conversation.

Mattermost versions 10.5.x <= 10.5.5, 9.11.x <= 9.11.15, 10.8.x <= 10.8.0, 10.7.x <= 10.7.2, 10.6.x <= 10.6.5 fail to properly enforce channel member management permissions when adding participants to playbook runs. This allows authenticated users with member-level permissions to bypass system admin restrictions and add or remove users to/from private channels via the playbook run participants feature, even when the 'Manage Members' permission has been explicitly removed. This can lead to unauthorized access to sensitive channel content and allow guest users to gain channel management privileges.

Mattermost fails to properly validate the permissions when soft deleting a team allowing a team member to soft delete other teams that they are not part of

Mattermost versions 10.5.x <= 10.5.2, 9.11.x <= 9.11.11 failed to properly verify a user's permissions when accessing groups, which allows an attacker to view group information via an API request.

Mattermost fails to update the permissions of the current session for a user who was just demoted to guest, allowing freshly demoted guests to change group names.

Mattermost fails to properly verify the permissions when managing/updating a bot allowing a User Manager role with user edit permissions to manage/update bots.

Mattermost fails to check whether a user is a guest when updating the tasks of a private playbook run allowing a guest to update the tasks of a private playbook run if they know the run ID.

Mattermost versions 10.5.x <= 10.5.4, 9.11.x <= 9.11.13 fail to properly restrict API access to team information, allowing guest users to bypass permissions and view information about public teams they are not members of via a direct API call to /api/v4/teams/{team_id}.

Mattermost fails to properly verify the permissions needed for viewing archived public channels,  allowing a member of one team to get details about the archived public channels of another team via the GET /api/v4/teams/<team-id>/channels/deleted endpoint.

Mattermost versions 10.7.x <= 10.7.0, 10.5.x <= 10.5.3, 9.11.x <= 9.11.12 fails to properly enforce access control restrictions for System Manager roles, allowing authenticated users with System Manager privileges to view team details they should not have access to via direct API requests to team endpoints, even when explicitly configured with 'No access' to Teams in the System Console.

Mattermost versions 10.5.x <= 10.5.5, 9.11.x <= 9.11.15, 10.8.x <= 10.8.0, 10.7.x <= 10.7.2, 10.6.x <= 10.6.5 fail to properly retrieve requestorInfo from playbooks handler for guest users which allows an attacker access to the playbook run.

Mattermost versions 10.5.x <= 10.5.5, 9.11.x <= 9.11.15, 10.8.x <= 10.8.0, 10.7.x <= 10.7.2, 10.6.x <= 10.6.5 fail to properly enforce channel member management permissions in playbook runs, allowing authenticated users without the 'Manage Channel Members' permission to add or remove users from public and private channels by manipulating playbook run participants when the run is linked to a channel.

Mattermost fails to properly validate the requesting user permissions when updating a system admin, allowing a user manager to update a system admin's details such as email, first name and last name.