Subdomain Takeover Made Easy: How to Detect Vulnerabilities Using Subdominator and SubSnipe

Introduction

In today’s interconnected digital world, one of the most overlooked but dangerous vulnerabilities is subdomain takeover. It’s a critical flaw that can allow attackers to hijack inactive or misconfigured subdomains, leading to phishing attacks, data theft, and brand reputation damage.

This blog will guide you step-by-step through what subdomain takeover is, how it works, and how you can detect and prevent it using two powerful, free, CLI-based tools: Subdominator and SubSnipe.

What is Subdomain Takeover?

Subdomain takeover occurs when a subdomain (like blog.example.com) is still pointing to a third-party service (like GitHub Pages, Heroku, or AWS), but that resource has been deleted or is no longer in use.

This misconfiguration leaves the subdomain open to exploitation. An attacker can claim the orphaned resource, effectively taking control of that subdomain and serving malicious content.

Example Scenario:

• You use blog.example.com and point it to GitHub Pages.
• Later, you delete the GitHub repository but forget to remove the DNS CNAME record.
• An attacker notices this and creates a new repo with the same name.
• Now, blog.example.com points to the attacker's content.

Scary? Absolutely.

Why Is This Dangerous?

• Phishing: Attackers can trick users into thinking the subdomain is trusted.
• Malware Hosting: Malware can be delivered under your brand name.
• Loss of Trust: Even one takeover incident can harm your reputation.

Tool 1: Subdominator

Subdominator is a powerful Go-based CLI tool that is fast, accurate, and great for scanning large lists of subdomains for takeover potential.

Key Features:

• Very fast (processes 100k records in under 20 minutes)
• Supports 90+ service fingerprints
• Validates vulnerable services in real-time

Installation:

GO111MODULE=on go install github.com/projectdiscovery/subdominator@latest

Basic Usage:

subdominator -l subdomains.txt -o results.txt --threads 100 --validate

Explanation:

• -l: Path to the file with subdomains
• -o: Output file
• --threads: Parallel scanning
• --validate: Actively checks if the service can be claimed

Tool 2: SubSnipe

SubSnipe is another CLI tool written in Go that not only detects vulnerable subdomains but also checks if the takeover is actually possible — making it highly reliable.

Key Features:

• Fingerprinting and validation combined
• Built-in support for popular providers (AWS, GitHub, etc.)
• Supports domain scan or subdomain file input

Installation:

git clone https://github.com/nsonaniya2010/SubSnipe.git
cd SubSnipe
chmod +x install.sh && ./install.sh

Basic Usage:

subsnipe -d example.com --output report.txt

OR

subsnipe -f subdomains.txt --output result.md

Explanation:

• -d: Scan domain for subdomains (uses crt.sh)
• -f: Provide your own list of subdomains
• --output: Save the result in the specified format

Best Practice Workflow:

1. Enumerate Subdomains using tools like Subfinder or Amass:

subfinder -d example.com -o subs.txt

2. Initial Scan with Subdominator:

subdominator -l subs.txt -o dom_results.txt --validate

3. Deep Validation using SubSnipe:

subsnipe -f subs.txt --output takeover_final.txt

4. Manual Review: Always verify before attempting any responsible disclosure.

Conclusion

Subdomain takeover is a silent killer in the cybersecurity world — often unnoticed until it’s too late. But with the right tools and practices, you can protect your assets and even identify takeover opportunities in bug bounty programs.

Subdominator offers blazing speed and accurate fingerprinting, while SubSnipe gives that extra layer of validation — together, they make a powerful combo in your InfoSec toolkit.

Keep scanning. Stay secure.

Author: Srimant Kumar
BLOG: Netrinix Solutions | @secure.with.sk