The plugin does not validate and escape some of its shortcode attributes before outputting them back in the page, which could allow users with a role as low as contributor to perform Stored Cross-Site Scripting attacks which could be used against high privilege users such as admins.
Exploit shortcode:
[wp_cart_button name='xss' price='1' button_text='" onmouseover="alert(1)" style="background:red;"']