The ConvertPlus plugin for WordPress is vulnerable to Deserialization of Untrusted Data in all versions up to, and including, 3.6.3 via the style parameter of the cpdisplaypreviewmodal AJAX action. The vulnerability exists because the action's nonce guard is gated behind an isset() check and fails open when the cpadminpagenonce parameter is omitted entirely, no capability check is performed on the callback, and sanitizetextfield() — applied to the $style value before it is concatenated directly into a shortcode string evaluated by doshortcode() — does not strip shortcode delimiters, allowing an attacker to inject a second, fully attacker-controlled [smilemodal] invocation that causes smilemodalpopup() to pass attacker-supplied base64-decoded bytes to maybeunserialize() with no allowedclasses restriction. This makes it possible for authenticated attackers, with Subscriber-level access and above, to inject a PHP object. No known POP chain is present in the vulnerable software, which means this vulnerability has no impact unless another plugin or theme containing a POP chain is installed on the site. If a POP chain is present via an additional plugin or theme installed on the target system, it may allow the attacker to perform actions like delete arbitrary files, retrieve sensitive data, or execute code depending on the POP chain present.

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 'settingsencoded' attribute of the 'smilemodal' 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.