Mattermost versions 10.4.x <= 10.4.2, 10.5.x <= 10.5.0, 9.11.x <= 9.11.10 fail to validate the uniqueness and quantity of task actions within the UpdateRunTaskActions GraphQL operation, which allows an attacker to create task items containing an excessive number of actions triggered by specific posts, overloading the server and leading to a denial-of-service (DoS) condition.
Mattermost versions 10.4.x <= 10.4.2, 10.5.x <= 10.5.0, 9.11.x <= 9.11.10 fail to properly validate the props used by the RetrospectivePost custom post type in the Playbooks plugin, which allows an attacker to create a specially crafted post with maliciously crafted props and cause a denial of service (DoS) of the web app for all users.
Mattermost versions 10.4.x <= 10.4.2, 10.5.x <= 10.5.0, 9.11.x <= 9.11.10 fail to properly validate permissions for the API endpoint /plugins/playbooks/api/v0/signal/keywords/ignore-thread, allowing any user or attacker to delete posts containing actions created by the Playbooks bot, even without channel access or appropriate permissions.