Mattermost versions 8.1.x before 8.1.10, 9.2.x before 9.2.6, 9.3.x before 9.3.2, and 9.4.x before 9.4.3 fail to correctly verify account ownership when switching from email to SAML authentication, allowing an authenticated attacker to take over other user accounts via a crafted switch request under specific conditions.

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 Server versions 9.5.x before 9.5.2, 9.4.x before 9.4.4, 9.3.x before 9.3.3, 8.1.x before 8.1.11 don't limit the number of user preferences which allows an attacker to send a large number of user preferences potentially causing denial of service.

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 versions shipped with Mattermost versions 8.1.x before 8.1.10, 9.2.x before 9.2.6, 9.3.x before 9.3.2, and 9.4.x before 9.4.3 fail to escape user-controlled outputs when generating HTML pages, which allows an attacker to perform reflected cross-site scripting attacks against the users of the Mattermost server.

Improper Access Control in Mattermost Server versions 9.5.x before 9.5.2, 9.4.x before 9.4.4, 9.3.x before 9.3.3, 8.1.x before 8.1.11 lacked proper access control in the /api/v4/users/me/teams endpoint allowing a team admin to get the invite ID of their team, thus allowing them to invite users, even if the "Add Members" permission was explicitly removed from team admins.

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 fails to check the "inviteguest" 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 versions 8.1.x before 8.1.9, 9.2.x before 9.2.5, 9.3.0, and 9.4.x before 9.4.2 fail to limit the number of role names requested from the API, allowing an authenticated attacker to cause the server to run out of memory and crash by issuing an unusually large HTTP request.

Mattermost versions 8.1.x before 8.1.10, 9.2.x before 9.2.6, 9.3.x before 9.3.2, and 9.4.x before 9.4.3 fail to limit the number of @-mentions processed per message, allowing an authenticated attacker to crash the client applications of other users via large, crafted messages.