The LearnPress plugin for WordPress is vulnerable to PHP Object Injection in versions up to, and including, 4.4.10 via deserialization of untrusted input from the 'checkout-email' request parameter during the checkout AJAX action. The value is passed through sanitize_text_field(), which does not strip serialized object syntax, then stored in the LearnPress session table and later fed to LP_Helper::maybe_unserialize() → unserialize() (without an allowed_classes restriction) by LP_Session_Handler::get() on subsequent requests. This makes it possible for unauthenticated attackers to inject a PHP Object.