DEV Community: Preston P

subdomain enumerator

Preston P — Mon, 17 Aug 2026 02:39:01 +0000

Finding Hidden Subdomains: Building a Subdomain Enumerator in Python

I recently built my third cybersecurity tool — a subdomain enumerator that finds hidden subdomains of a target domain. Here's how I built it.

What Is a Subdomain Enumerator?

A subdomain enumerator finds all the subdomains of a domain. For example:

www.example.com
mail.example.com
admin.example.com
dev.example.com

How It Works

Loads a wordlist of common subdomain names
Tries to resolve each one using DNS
Prints the ones that exist

The Code

Get a list of common subdomains (from a wordlist file)
For each subdomain, combine it with the target domain
Try to resolve it to an IP address using DNS
If it resolves → the subdomain exists!
Print it and save it

What I Learned

I learned that subdomains are important in the field of cybersecurity since it relates to ethical hacking. Defenders use this to find weak points and find out what to protect. In this project I also learned how the internet works with this code.

The Full Code

notserp55 / subdomain-enumerator

A tool that finds all subdomains of a target domain.

🔍 Subdomain Enumerator

A powerful, multi-threaded subdomain enumeration tool written in Python. Find all subdomains of a target domain using DNS resolution and HTTP checks.

🎯 What It Does

A subdomain enumerator finds all the subdomains associated with a target domain.

Why This Matters

Use Case	Explanation
🔐 Security Research	Discover attack surfaces and hidden services
🔎 OSINT	Gather public information about a target
🐛 Bug Bounty	Find subdomains for vulnerability testing
🛡️ Defensive Security	Identify unauthorized or forgotten services
📊 Asset Discovery	Know what you own and need to protect

✨ Features

Feature	Description
🚀 Multi-threaded	Fast scanning using concurrent threads
🌐 DNS Resolution	Checks if subdomains actually exist
🌍 HTTP/HTTPS Detection	Identifies if subdomains have websites
📝 Custom Wordlist Support	Use your own subdomain list
💻 Command-Line Interface	Professional tool design
💾 Results Saving	Automatically saves findings to a file
🛡️ Error Handling	Graceful handling of DNS failures

…

View on GitHub

Password Checker

Preston P — Wed, 15 Jul 2026 21:50:43 +0000

Building a Password Checker: Strength + Breach Detection in Python

I recently built my second cybersecurity tool — a password checker that does two things: analyzes password strength AND checks if it's been leaked in a data breach. Here's how I built it.

The Inspiration

After building my first tool (a multi-threaded port scanner), I wanted to tackle something directly related to everyday security. Passwords are everywhere, and most people don't know if their passwords are strong or if they've been exposed in a breach.

I wanted to build a tool that would answer two questions:

Is this password strong?
Has this password been leaked?

What It Does

🔐 1. Strength Analysis

The tool checks five criteria and gives a score from 0-6:

Criteria	Points
Length (12+ characters)	+2
Length (8-11 characters)	+1
Uppercase letters	+1
Lowercase letters	+1
Numbers	+1
Symbols (!@#$%^&*)	+1

Score Interpretation:

Score	Rating
5-6	🟢 GREAT
4	🟢 GOOD
3	🟡 DECENT
0-2	🔴 WEAK

🛡️ 2. Breach Detection

The tool checks the HaveIBeenPwned API to see if your password appears in any known data breaches.

How it stays secure:

Your password is never sent over the internet
Only the first 5 characters of the SHA-1 hash are sent
This is called k-anonymity — the API never sees your full password

Conclusion
Building this password checker taught me a lot about:

Working with APIs

Cryptographic hashing

Privacy-first design

Creating useful, user-friendly tools

If you're learning cybersecurity or Python, I highly recommend building tools like this. You learn far more than you would from following tutorials alone.

This is my second cybersecurity project. If I can build it, so can you. 🚀

Port scanner Project

Preston P — Thu, 09 Jul 2026 04:26:20 +0000

Building My First Cybersecurity Tool:

A Multi-Threaded Port Scanner in Python

A few weeks ago, I didn't know what a port was. Today, I built a tool that can scan 1,000 ports in under 10 seconds. Here's how I did it.

The Backstory

I'm a high school student interested in cybersecurity, and I wanted to build something real. Not just follow a tutorial, but actually create a tool from scratch.

I decided to build a port scanner because:

It's a fundamental cybersecurity tool
It would teach me networking basics
I could use what I learned in Python class (AP CSP)
I wanted something to put on my GitHub

This is what I built:

** What Is a Port Scanner?**

Think of a computer like a huge apartment building with 1,000 numbered doors (ports). Each door leads to a different service:

Port	Service
80	Websites (HTTP)
443	Secure websites (HTTPS)
22	Remote access (SSH)
3306	Databases (MySQL)

A port scanner "knocks" on each door to see which ones are open. If a door is open, there might be a service running that could be a security risk (or just something useful!).

Conclusion
Building this port scanner taught me more than any textbook could. If you're interested in cybersecurity, I highly recommend building your own tools — it's the best way to understand how things actually work.

Thanks for reading! Feel free to ask questions or suggest improvements.