s3enum is a tool to enumerate a target's Amazon S3 buckets. It is fast and leverages DNS instead of HTTP, which means that requests don't hit AWS directly.
It was originally built back in 2016 to target GitHub.

Installation

Binaries
Find the binaries on the Releases page.

Go

Usage
You need to specify the base name of the target (e.g. hackerone), and a word list. You could either use the example wordlist.txt file from this repository, or get a word list elsewhere. Optionally, you could specify the number of threads (defaults to 10).

$ s3enum --wordlist examples/wordlist.txt --suffixlist examples/suffixlist.txt --threads 10 hackerone
 
 hackerone
 hackerone-attachment
 hackerone-attachments
 hackerone-static
 hackerone-upload

By default s3enum will use the name server as specified in /etc/resolv.conf. Alternatively, you could specify a different name server using the --nameserver option. Besides, you could test multiple names at the same time.

s3enum \
   --wordlist examples/wordlist.txt \
   --suffixlist examples/suffixlist.txt \
   --nameserver 1.1.1.1 \
   hackerone h1 roflcopter