bigcommerce CDN names extend past cdn[12] and include: cdn.bigcommerce.com cdn1.bigcommerce.com cdn2.bigcommerce.com cdn3.bigcommerce.com cdn4.bigcommerce.com and more. A more appropriate match would be: ^cdn\d*\.bigcommerce\.com$ Leaking of bigcommerce.com CDN URLs can result very detailed tracking of items people are looking to buy, purchases etc for any stores run by them. This seems to be the case even for stores that use bigcommerce.com but that use their own domain name.