Shopify: Subdomain Takeover - https://competition.shopify.com/

Dear Shopify Security Team, The Shopify.com subdomain competition.shopify.com was vulnerable to a subdomain takeover as it was pointing to an unclaimed Heroku service through the CNAME competition.shopify.com.herokudns.com, while the custom domain 'competition.shopify.com' was unclaimed in Heroku...