Simple Membership < 4.4.4 - Authenticated(Contributor+) Stored Cross-Site Scripting via Shortcode

Description

The Simple Membership plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's 'swpm_paypal_subscription_cancel_link' shortcode in all versions up to, and including, 4.4.3 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.