Read the proper write-up here: https://publish.whoisbinit.me/amazon-ec2-dangling-dns-records-on-surf-test-xwf-internet-org!
In this GitHub Gist, I have included my script (main.sh), which I used in discovering this vulnerability.
The script performs sub-domain enumeration over the Internet.org domain using assetfinder, subfinder, sublist3r and amass, and then checks for sub-domains which are further pointing to Amazon EC2 hostnames, and stores all of the results in multiple text files.
I didn't perform any form of manual work in discovering this vulnerability, and my workflow was fully automated with the help of Bash scripting using different tools.