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.
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.
An issue was discovered in Mattermost Server before 5.1. It allows attackers to bypass intended access restrictions (for group-message channel creation) via the Group message slash command.