The Tutor LMS – eLearning and online course solution plugin for WordPress is vulnerable to PHP Object Injection in all versions up to, and including, 4.0.7 via the withdrawmethodfield parameter of the tutorsavewithdrawaccount AJAX handler. This is due to the handler lacking any capability or role check, relying solely on a nonce, while also passing attacker-supplied values through escsql(), which replaces every % character with a 66-byte HMAC placeholder token before the data is serialized and stored via updateusermeta(); when the meta is later retrieved, the placeholder is collapsed back to a single %, leaving serialized string length declarations 65 bytes greater than the actual content, and because array keys originate from entirely unescaped POST field names, unserialize() over-reads into attacker-controlled bytes, allowing injection of an arbitrary serialized object stream. This makes it possible for authenticated attackers, with subscriber-level access and above, to achieve remote code execution on the server by triggering the GuzzleHttp\Cookie\FileCookieJar POP chain, reachable via the splautoloadregister loader in TUTOR\RestAPI which loads the plugin's own bundled PayPal Composer autoloader, writing attacker-controlled content to an attacker-specified filename. This has an unauthenticated pathway when user registration is enabled, which is common for students and teachers to register, and it requires the monetization feature to be enabled.