The Frontend User Notes plugin for WordPress is vulnerable to Cross-Site Request Forgery in all versions up to, and including, 2.1.1. This is due to missing or incorrect nonce validation on the funp_ajax_modify_notes function. This makes it possible for unauthenticated attackers to trick a logged-in user into visiting a malicious page, causing unauthorized overwriting of that victim's own note content via a forged cross-site request to wp_update_post() via a forged request granted they can trick a site administrator into performing an action such as clicking on a link. Due to ownership enforcement comparing the note's stored _funp_single_user_id meta against the current session's user ID, the attack is limited to modifying only notes belonging to the tricked victim, and cannot be used to alter notes owned by arbitrary third-party users.