The Welcart e-Commerce plugin for WordPress is vulnerable to Stored Cross-Site Scripting via Settlement Notification Parameters in all versions up to, and including, 2.12.2 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 IPN endpoint accepts the 'rel' and 'option' parameters with no authentication, nonce validation, or signature verification, meaning any unauthenticated attacker can directly submit malicious payloads that are stored and later rendered in the administrator's settlement error log view.