An issue was discovered in Mattermost Server before 3.0.0. It allows attackers to obtain sensitive information about team URLs via an API.

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

An issue was discovered in Mattermost Server before 4.2.0, 4.1.1, and 4.0.5. It allows attackers to obtain sensitive information (user statuses) via a REST API version 4 endpoint.

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. It discloses the team creator's e-mail address to members.

An issue was discovered in Mattermost Server before 4.1.0, 4.0.4, and 3.10.3. It allows attackers to discover a team invite ID by requesting a JSON document.

An issue was discovered in Mattermost Server before 4.1.0, 4.0.4, and 3.10.3. It allows attackers to discover team invite IDs via team API endpoints.

An issue was discovered in Mattermost Server before 3.2.0. Attackers could read LDAP fields via injection.

An issue was discovered in Mattermost Mobile Apps before 1.26.0. A view cache can persist on a device after a logout.

An issue was discovered in Mattermost Mobile Apps before 1.26.0. Cookie data can persist on a device after a logout.

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 a role change.

An issue was discovered in Mattermost Server before 3.0.0. It does not ensure that a cookie is used over SSL.

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 about whether someone has 2FA enabled.

An issue was discovered in Mattermost Server before 5.15.0. Login access control can be bypassed via crafted input.

An issue was discovered in Mattermost Server before 5.16.1, 5.15.2, 5.14.5, and 5.9.6. It allows attackers to obtain sensitive information (local files) during legacy attachment migration.

An issue was discovered in Mattermost Server before 5.8.0. It does not always generate a robots.txt file.

An issue was discovered in Mattermost Server before 5.12.0. Use of a Proxy HTTP header, rather than the source address in an IP packet header, for obtaining IP address information was mishandled.

An issue was discovered in Mattermost Server before 5.18.0. It has weak permissions for server-local file storage.

An issue was discovered in Mattermost Mobile Apps before 1.26.0. Local logging is not blocked for sensitive information (e.g., server addresses or message content).

Mattermost fails to sanitize post metadata during audit logging resulting in permalinks contents being logged

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 board blocks when importing boards which allows an attacker could read any arbitrary file on the system via importing and exporting a specially crafted import archive in Boards.

An issue was discovered in Mattermost Server before 5.18.0, 5.17.2, 5.16.4, 5.15.4, and 5.9.7. There are weak permissions for configuration files.

Mattermost fails to delete card attachments in Boards, allowing an attacker to access deleted attachments.

Mattermost 6.0.2 and earlier fails to sufficiently sanitize user's password in audit logs when user creation fails.

Mattermost Boards plugin v0.10.0 and earlier fails to invalidate a session on the server-side when a user logged out of Boards, which allows an attacker to reuse old session token for authorization.

Mattermost Mobile Apps versions <=2.25.0  fail to terminate sessions during logout under certain conditions (e.g. poor connectivity), allowing unauthorized users on shared devices to access sensitive notification content via continued mobile notifications

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. mmctl allows directory traversal via HTTP, aka MMSA-2020-0014.

An issue was discovered in Mattermost Mobile Apps before 1.29.0. The iOS app allowed Single Sign-On cookies and Local Storage to remain after a logout, aka MMSA-2020-0013.

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 Mobile Apps before 1.30.0. Authorization tokens can sometimes be disclosed to third-party servers, aka MMSA-2020-0018.

An issue was discovered in Mattermost Mobile Apps before 1.31.2 on iOS. Unintended third-party servers could sometimes obtain authorization tokens, aka MMSA-2020-0022.

An issue was discovered in Mattermost Server before 5.4.0. It mishandles possession of superfluous authentication credentials.

An issue was discovered in Mattermost Server before 3.8.2, 3.7.5, and 3.6.7. Weak hashing was used for e-mail invitations, OAuth, and e-mail verification tokens.

An issue was discovered in Mattermost Server before 3.9.0 when SAML is used. Encryption and signature verification are not mandatory.

Mattermost versions <11 fail to enforce multi-factor authentication on WebSocket connections which allows unauthenticated users to access sensitive information via WebSocket events

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

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.

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to sanitize sensitive configuration fields before including them in support packet generation, which allows a Mattermost System Admin or any party with access to a support packet to obtain sensitive credentials in plaintext via downloading a support packet from the System Console.. Mattermost Advisory ID: MMSA-2026-00607

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 fails to honor the ShowEmailAddress setting when constructing a response to the /api/v4/users/me/teams API endpoint, allowing an attacker with team admin privileges to learn the team owner's email address in the response.

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to sanitize team member data when returned via API to users without elevated permissions which allows a user without permissions to get data about team members roles via invoking various team API endpoints.. Mattermost Advisory ID: MMSA-2026-00626

Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to sanitize sensitive data in WebSocket messages which allows authenticated users to exfiltrate password hashes and MFA secrets via profile nickname updates or email verification events. Mattermost Advisory ID: MMSA-2025-00560

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to restrict role_updated websocket event broadcasts to members of the affected team or channel which allows an authenticated attacker with guest-level access to observe permission scheme change notifications for private teams they are not a member of via the websocket connection.. Mattermost Advisory ID: MMSA-2026-00616

Mattermost versions 11.0.x <= 11.0.2, 10.12.x <= 10.12.1, 10.11.x <= 10.11.4, 10.5.x <= 10.5.12 fail to sanitize team email addresses to be visible only to Team Admins, which allows any authenticated user to view team email addresses via the GET /api/v4/channels/{channel_id}/common_teams endpoint

Mattermost versions 10.11.x <= 10.11.3, 10.5.x <= 10.5.11, 10.12.x <= 10.12.0 fail to sanitize user data which allows system administrators to access password hashes and MFA secrets via the POST /api/v4/users/{user_id}/email/verify/member endpoint

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to sanitize sensitive configuration fields in the Mattermost Calls plugin which allows an attacker with access to a support packet to obtain TURN server credentials via the plaintext values present in the exported plugin configuration.. Mattermost Advisory ID: MMSA-2026-00605

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to validate that a username returned during bot registration belongs to a bot account, which allows an unprivileged attacker to intercept private messages sent by plugins via direct message channels by pre-registering a user account with a predictable plugin bot username.. Mattermost Advisory ID: MMSA-2026-00649

Mattermost fails to honor the ShowEmailAddress setting when constructing a response to the "Regenerate Invite Id" API endpoint, allowing an attacker with team admin privileges to learn the team owner's email address in the response.

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.