Unrelated forum topic deletion via cascading foreign key

Improper topic deletion in NamelessMC Nameless before 2.2.0 allows remote authenticated users to cause deletion of unrelated forum content. The nl2_topics.topic_last_user foreign key uses ON DELETE CASCADE, so deleting a user row removes every topic whose last-user reference points to that account and then removes the topic's posts. An attacker must post in other users' topics and an administrator must delete the attacker's account; the result is deletion of unrelated topics and comments.