An issue was discovered in Mattermost Server before 3.0.2. The purposes of a session ID and a Session Token were mishandled.

Mattermost versions 10.11.x <= 10.11.12, 11.5.x <= 11.5.0, 11.4.x <= 11.4.2, 11.3.x <= 11.3.2 fail to enforce atomic single-use consumption of guest magic link tokens, which allows an attacker with access to a valid magic link to establish multiple independent authenticated sessions via concurrent requests.. Mattermost Advisory ID: MMSA-2026-00624

Mattermost Desktop App versions <=5.8.0 fail to sufficiently configure Electron Fuses which allows an attacker to gather Chromium cookies or abuse other misconfigurations via remote/local access.

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 ensure that remote/synthetic users cannot create sessions or reset passwords, which allows the munged email addresses, created by shared channels, to be used to receive email notifications and to reset passwords, when they are valid, functional emails.

Mattermost versions 9.5.x <= 9.5.3, 9.6.x <= 9.6.1 and 8.1.x <= 8.1.12 fail to perform proper authorization checks which allows a member running a playbook in an existing channel to be promoted to a channel admin

Mattermost version 6.4.x and earlier fails to properly check the plugin version when a plugin is installed from the Marketplace, which allows an authenticated and an authorized user to install and exploit an old plugin version from the Marketplace which might have known vulnerabilities.

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 enforce PermissionInviteUser when setting AllowOpenInvite or AllowedDomains during team creation (the check was only applied on update/patch), which allows an authenticated user holding PermissionCreateTeam but not PermissionInviteUser on the resulting team to configure invite-controlled team settings (make the team publicly joinable via open invite and/or constrain membership via allowed domains) that they are not permitted to set on an existing team via POST /api/v4/teams with allow_open_invite: true and/or a non-empty allowed_domains in the request body.. Mattermost Advisory ID: MMSA-2026-00655

Mattermost versions 10.11.x <= 10.11.1, 10.10.x <= 10.10.2, 10.5.x <= 10.5.10 fail to verify a user has permission to join a Mattermost team using the original invite token which allows any attacked to join any team on a Mattermost server regardless of restrictions via manipulating the OAuth state.

Mattermost Confluence Plugin version <1.5.0 fails to check the access of the user to the Confluence space which allows attackers to create a subscription for a Confluence space the user does not have access to via the create subscription endpoint.

Mattermost Confluence Plugin version <1.5.0 fails to check the access of the user to the channel which allows attackers to get channel subscription details without proper access to the channel via API call to the GET autocomplete/GetChannelSubscriptions endpoint.

Mattermost Confluence Plugin version <1.5.0 fails to check the access of the user to the channel which allows attackers to create a channel subscription without proper access to the channel via API call to the edit channel subscription endpoint.

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. 

Mattermost Confluence Plugin version <1.5.0 fails to check the access of the user to the Confluence space which allows attackers to edit a subscription for a Confluence space the user does not have access for via edit subscription endpoint.

Mattermost Confluence Plugin version <1.5.0 fails to enforce authentication of the user to the Mattermost instance which allows unauthenticated attackers to access subscription details without via API call to GET subscription endpoint.

Mattermost Confluence Plugin version <1.5.0 fails to check the access of the user to the channel which allows attackers to get channel subscription details without proper access to the channel via API call to the Get Channel Subscriptions details endpoint.

Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to check the create_post channel permission during post edit operations which allows an authenticated attacker with revoked posting privileges to modify their existing posts via direct API requests to the post update and patch endpoints.. Mattermost Advisory ID: MMSA-2026-00627

Mattermost Plugin Legal Hold versions <=1.1.4 fail to halt request processing after a failed authorization check in ServeHTTP which allows an authenticated attacker to access, create, download, and delete legal hold data via crafted API requests to the plugin's endpoints. Mattermost Advisory ID: MMSA-2026-00621

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to filter invite IDs based on user permissions, which allows regular users to bypass access control restrictions and register unauthorized accounts via leaked invite IDs during team creation.. Mattermost Advisory ID: MMSA-2025-00565

Mattermost versions 10.10.x <= 10.10.2, 10.5.x <= 10.5.10, 10.11.x <= 10.11.2 fail to validate email ownership during Slack import process which allows attackers to create verified user accounts with arbitrary email domains via malicious Slack import data to bypass email-based team access restrictions

Mattermost versions 10.5.x <= 10.5.12, 10.11.x <= 10.11.2 fail to properly validate guest user permissions when accessing channel information which allows guest users to discover active public channels and their metadata via the `/api/v4/teams/{team_id}/channels/ids` endpoint

Mattermost Plugins versions <=11.5 11.1.5 10.13.11 11.3.4.0 fail to properly check for permissions when processing commands in the Gitlab plugin which allows normal users to uninstall instances or setup webhook connections via the {{gitlab instance {option}}} or the {{/gitlab webhook {option}}} commands. Mattermost Advisory ID: MMSA-2026-00600

Mattermost versions 10.11.x <= 10.11.12 fail to validate whether users were correctly owned by the correct Connected Workspace which allows a malicious remote server connected using the Conntexted Workspaces feature to change the displayed status of local users via the Connected Workspaces API.. Mattermost Advisory ID: MMSA-2026-00603

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to properly validate team membership when searching channels which allows a removed team member to enumerate all public channels within a private team via the channel search API endpoint.. Mattermost Advisory ID: MMSA-2025-00568

Mattermost fails to properly check the creator of an attached file when adding the file to a draft post, potentially exposing unauthorized file information.

Mattermost versions 10.11.x <= 10.11.9 fail to enforce invite permissions when updating team settings, which allows team administrators without proper permissions to bypass restrictions and add users to their team via API requests. Mattermost Advisory ID: MMSA-2025-00561

Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to properly validate team membership when processing channel mentions which allows authenticated users to determine the existence of teams and their URL names via posting channel shortlinks and observing the channel_mentions property in the API response. Mattermost Advisory ID: MMSA-2025-00563

Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 and Mattermost Plugin Zoom versions <=1.11.0 fail to validate user identity and post ownership in the {{/api/v1/askPMI}} endpoint which allows unauthorized users to start Zoom meetings as any user and overwrite arbitrary posts via direct API calls with manipulated user IDs and post data.. Mattermost Advisory ID: MMSA-2025-00534

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.

Mattermost versions 10.10.x <= 10.10.1 fail to properly sanitize user data during shared channel membership synchronization, which allows malicious or compromised remote clusters to access sensitive user information via unsanitized user objects. This vulnerability affects Mattermost Server instances with shared channels enabled.

Mattermost Confluence Plugin version <1.5.0 fails to check the access of the user to the channel which allows attackers to create channel subscription without proper access to the channel via API call to the create channel subscription endpoint.

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

Mattermost fails to verify if the requestor is a sysadmin or not, before allowing `install` requests to the Apps allowing a regular user send install requests to the Apps.

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 fails to properly check the permissions when executing commands allowing a member with no permissions to post a message in a channel to actually post it by executing channel commands.

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

When creating a playbook run via the /dialog API, Mattermost fails to validate all parameters, allowing an authenticated attacker to edit an arbitrary channel post.

Mattermost Apps Framework fails to verify that a secret provided in the incoming webhook request allowing an attacker to modify the contents of the post sent by the Apps.

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.

A missing permissions check in Mattermost Playbooks in Mattermost allows an attacker to modify a playbook via the /plugins/playbooks/api/v0/playbooks/[playbookID] API.

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 invalidate existing authorization codes when deauthorizing an OAuth2 app, allowing an attacker possessing an authorization code to generate an access token.

When processing an email invite to a private channel on a team, Mattermost fails to validate the inviter's permission to that channel, allowing an attacker to invite themselves to a private channel.

Mattermost versions 9.10.x <= 9.10.2, 9.11.x <= 9.11.1, 9.5.x <= 9.5.9 fail to check that the origin of the message in an integration action matches with the original post metadata which allows an authenticated user to delete an arbitrary post.

An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended access restrictions (for setting a channel header) via the Channel header slash command API.

An issue was discovered in Mattermost Server before 5.2 and 5.1.1. Authorization could be bypassed if the channel name were not the same in the params and the body.

Mattermost versions 10.11.x <= 10.11.1, 10.10.x <= 10.10.2, 10.5.x <= 10.5.10 fail to verify a user has permission to join a Mattermost team using the original invite token which allows any attacked to join any team on a Mattermost server regardless of restrictions via manipulating the RelayState

Mattermost fails to delete the attachments when deleting a message in a thread allowing a simple user to still be able to access and download the attachment of a deleted message

Missing Authorization vulnerability in WPDeveloper EmbedPress allows Exploiting Incorrectly Configured Access Control Security Levels.This issue affects EmbedPress: from n/a through 4.0.4.

Missing Authorization vulnerability in WPZOOM Recipe Card Blocks for Gutenberg & Elementor recipe-card-blocks-by-wpzoom.This issue affects Recipe Card Blocks for Gutenberg & Elementor: from n/a through <= 3.4.8.