CorvusPay WooCommerce Payment Gateway <= 2.7.4 - Unauthenticated Stored Cross-Site Scripting via 'approval_code' Parameter

The CorvusPay WooCommerce Payment Gateway plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'approval_code' parameter in all versions up to, and including, 2.7.4 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 unauthenticated REST endpoint POST /wp-json/corvuspay/success/ is registered with permission_callback set to __return_true, and although a signature validation step exists it only logs the result without halting execution, meaning an attacker can supply a completely arbitrary signature and have a malicious approval_code stored in the database unchallenged.