Custom Payment Gateways for WooCommerce <= 2.1.0 - Unauthenticated Stored Cross-Site Scripting via 'alg_wc_cpg_input_fields' Parameter

The Custom Payment Gateways for WooCommerce plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'alg_wc_cpg_input_fields' parameter in all versions up to, and including, 2.1.0 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. This vulnerability is exploitable by unauthenticated guest users submitting a crafted checkout POST request, requiring no custom input fields to be configured in the plugin.