Mattermost Playbooks fails to properly validate the props used by the RetrospectivePost custom post type

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 servi...