The Co-Authors, Multiple Authors and Guest Authors in an Author Box with PublishPress Authors plugin for WordPress is vulnerable to Insecure Direct Object Reference to Privilege Escalation/Account Takeover in all versions up to, and including, 4.7.1 via the action_edited_author() due to missing validation on the 'authors-user_id' user controlled key. This makes it possible for authenticated attackers, with Author-level access and above, to update arbitrary user accounts email addresses, including administrators, which can then be leveraged to reset that user's account password and gain access.
The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.