The ConvertPlus plugin for WordPress is vulnerable to PHP Object Injection in all versions up to, and including, 3.5.26 via deserialization of untrusted input from the settings_encoded attribute of the smile_modal shortcode. This makes it possible for authenticated attackers, with contributor-level access and above, to inject a PHP Object. No POP chain is present in the vulnerable plugin. If a POP chain is present via an additional plugin or theme installed on the target system, it could allow the attacker to delete arbitrary files, retrieve sensitive data, or execute code.