The Tutor LMS – eLearning and online course solution plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 4.1.2 via the init_routes due to missing validation on a user controlled key. This makes it possible for authenticated attackers, with subscriber-level access and above, to read paid course lesson and topic content without enrollment, retrieve quiz answer keys including the is_correct field before attempting a quiz, and enumerate the email addresses, usernames, and registration data of other users including instructors and administrators. Exploitation requires that the attacker hold a valid Tutor LMS API key/secret pair, which is issued to subscriber-level users through the plugin's API key management feature.