Burp Suite extension to discover assets from HTTP response using passive scanning. Refer our blog Asset Discovery using Burp Suite for more details.
The extension is now part of the BApp store and can be installed directly from the Burp Suite. https://portswigger.net/bappstore/d927f0065171485981d6eb49a860fc3e
Passively parses HTTP response of the URLs in scope and identifies different type assets such as domain, subdomain, IP, S3 bucket etc. and lists them as informational issues.
A large portion of the base code has been taken from the following sources: