Pentest Subdomain Enumeration Using Rapiddns.io

[dEEpEst]

Subdomain Enumeration Using Rapiddns.io

Function​

function rapiddns() {
  curl -s "https://rapiddns.io/subdomain/$1?full=1" | grep -oE "[\.a-zA-Z0-9-]+\.$1" | tr '[:upper:]' '[:lower:]' | sort -u
}

Using the Terminal (Current Session)​

If you ran the function definition in the terminal, you can use it directly:

rapiddns example.com

This will make a request to

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, will extract subdomains, convert them to lowercase, and sort them by removing duplicates.

Use in a Bash Script​

If you want the function to be available in a script, save it in a file, for example rapiddns.sh :

#!/bin/bash

function rapiddns() {
  curl -s "https://rapiddns.io/subdomain/$1?full=1" | grep -oE "[\.a-zA-Z0-9-]+\.$1" | tr '[:upper:]' '[:lower:]' | sort -u
}

rapiddns "$1"

Then, give it execute permissions and use it:

chmod +x rapiddns.sh
./rapiddns.sh example.com

Permanent Use on your System​

If you want rapiddns to always be available without having to define it each time, add it to your shell configuration file:

1. For Bash (used on most Linux systems):

nano ~/.bashrc

Then, add the function to the end of the file and save the changes (Ctrl + X, then Y and Enter).


2. For Zsh (if you use zsh, such as on macOS or Kali Linux):

nano ~/.zshrc

Add the function at the end and save.


3. Load changes without restarting the terminal:

source ~/.bashrc  # For Bash
source ~/.zshrc   # For Zsh

Now you can use rapiddns on any terminal with:

rapiddns example.com

Context of Use​

• It is used to list subdomains of any given domain.
• It is useful in security testing, information gathering, and pentesting.
• You can combine it with other tools like httprobe, aquatone, or nmap for more detailed analysis.

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Disclaimer: The content shared in this forum is for educational and informational purposes only. We promote ethical cybersecurity practices and do not support or condone any illegal activities. Any misuse of the information provided is solely the responsibility of the user. Always ensure compliance with local laws and ethical guidelines when conducting security research.

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