ShopLentor <= 3.3.7 - Authenticated (Administrator+) Arbitrary Function Execution via 'callback' Parameter via REST API

The ShopLentor plugin for WordPress is vulnerable to arbitrary function execution via the woolentoropt/v1/custom-action REST API endpoint in all versions up to, and including, 3.3.7. This is due to the handle_action() method passing user-supplied input directly to call_user_func() without an allowlist of permitted callbacks. This makes it possible for authenticated attackers, with Administrator-level access and above, to execute arbitrary PHP callable functions via the 'callback' parameter.