The plugin does not validate and escape some of its shortcode attributes before outputting them back in a page/post where the shortcode is embed, which could allow users with the contributor role and above to perform Stored Cross-Site Scripting attacks.
[wp_paypal_payment_box_for_any_amount email='[email protected]' description='XSS' cbt='" accesskey="X" onclick="alert(1)"']
Click Alt + Shift + X in Firefox to trigger the XSS.
More information about access keys: https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/accesskey