The WPC Product Options for WooCommerce plugin for WordPress is vulnerable to Stored Cross-Site Scripting via wpcpo-* Array Key via Multipart Field Name in all versions up to, and including, 4.0.5 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. This is exploitable via guest checkout without authentication because the malicious payload is embedded in a multipart Content-Disposition field name beginning with 'wpcpo-', which PHP's RFC1867 parser preserves byte-for-byte and stores into order item meta.