Update aws-s3-unauthenticated-enum.md

[olizimmermann]

📦 Add s3dns – Passive DNS-Based Cloud Bucket Discovery Tool

Summary:

This PR adds s3dns under the "Enumeration & OSINT" section of the AWS - S3 Unauthenticated Enum guide.

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About the Tool:

s3dns is a lightweight DNS server designed to passively detect cloud storage buckets (AWS S3, Google Cloud Storage, Azure Blob) during reconnaissance.
It analyzes DNS traffic, follows CNAME chains, checks IP ranges, and matches against known bucket patterns — all without brute-forcing or direct API calls.

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Why this belongs in the guide:

• Enhances the passive enumeration section with a DNS-layer detection approach
• Complements existing tips like CNAME checks and GrayhatWarfare lookups
• Useful for stealthy recon and early detection during OSINT workflows

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Repository: https://github.com/olizimmermann/s3dns