Custom User Profile Fields for User Registration & Member Frontend Profiles with Paid Memberships Pro < 1.8.1 - Contributor+ Stored XSS via Shortcode

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.

PoC

Exploit shortcode: [pmpro_signup button=‘XSS" onmouseover=“alert(1)”’] Dependency: Paid Memberships Pro plugin - https://wordpress.org/plugins/paid-memberships-pro