The Simple Membership WordPress plugin before 4.2.2 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.

The Simple Membership WordPress plugin before 4.1.3 allows user to change their membership at the registration stage due to insufficient checking of a user supplied parameter.

The Simple Membership WordPress plugin before 4.1.3 does not properly validate the membershiplevel parameter when editing a profile, allowing members to escalate to a higher membership level by using a crafted POST request.

The Simple Membership WordPress plugin before 4.1.1 does not properly sanitise and escape parameters before outputting them back in AJAX actions, leading to Reflected Cross-Site Scripting

The Simple Membership WordPress plugin before 4.1.0 does not have CSRF check in place when deleting Transactions, which could allow attackers to make a logged in admin delete arbitrary transactions via a CSRF attack

The Simple Membership WordPress plugin before 4.0.9 does not have CSRF check when deleting members in bulk, which could allow attackers to make a logged in admin delete them via a CSRF attack

The simple-membership plugin before 3.5.7 for WordPress has XSS.

The Simple Membership plugin before 3.8.5 for WordPress has CSRF affecting the Bulk Operation section.