Welcart e-Commerce <= 2.12.5 - Unauthenticated Stored Cross-Site Scripting via 'gid' Parameter

The Welcart e-Commerce plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'gid' parameter in all versions up to, and including, 2.12.5 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The payload is staged by an unauthenticated visitor who forges the ROBOT PAYMENT browser-return request, storing the malicious gid value in order metadata; the script then fires when an administrator opens that order in the WordPress admin panel.