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👋 Hey, I'm Vipul

I'm a cybersecurity enthusiast and the writer behind The Hacker's Log — where I break down how real hackers think, find, and exploit vulnerabilities (ethically, of course 😎).

In today's deep-dive, let's uncover one of the most powerful — yet underrated — hacker secrets: Hidden API Endpoints.

Hackers' Recon Guide (detailed, practical, downloadable) → https://thehackerslog.gumroad.com/l/hackersreconguide

🧩 What Are Hidden API Endpoints?

Every web app relies on APIs — those invisible bridges connecting your clicks to the database. But here's the twist: not all endpoints are visible. Some are hidden or undocumented, like:

  • /api/v2/internal/users
  • /api/admin/deleteUser
  • /api/dev/test_endpoint

These are internal routes developers use for debugging, testing, or staging environments. They often don't appear on the UI, but they still respond if you know where to knock. 🚪

And that's what makes them gold for bug bounty hunters and pentesters.

🧠 The Hacker Mindset: Think Like a Developer

Hidden endpoints exist because of developer habits.

When building an app, developers:

  • Keep staging APIs live even after launch 🧱
  • Forget to delete debug or admin routes 🧑‍💻
  • Leave unlinked endpoints for mobile or internal dashboards 📱

So, instead of just scanning websites like a robot, you need to think like a dev.

Ask yourself:

"If I built this feature, what would I name the endpoint?"

That's how you start finding the invisible attack surface.

🕵️ Step 1: Passive Recon — Finding the Clues

Passive recon means collecting data without sending aggressive requests. Here's how I do it 👇

🔍 Look Inside JavaScript Files

Developers often hardcode API URLs or endpoints inside .js files.

Use LinkFinder — a tool that extracts endpoints from JavaScript.

# Clone and run LinkFinder
git clone https://github.com/GerbenJavado/LinkFinder.git
cd LinkFinder
python3 linkfinder.py -i https://target.com/static/main.js -o cli

It'll output URLs like:

/api/v1/users
/api/internal/logs
/api/admin/backup

Congrats 🎉 — you've just found hidden paths without touching the server.

🕸️ Crawl Archived Pages

The Wayback Machine stores old URLs that developers forgot about.

Use this tool combo:

echo "target.com" | waybackurls | grep "/api/"

That one line can reveal long-lost routes like:

https://target.com/api/v1/test
https://target.com/api/dev/login

Sometimes, these are still alive. 🧟

⚙️ Step 2: Active Discovery — Knocking on the Door

Once you've collected endpoint candidates, it's time to test them safely.

You can use curl or automated tools like ffuf.

🧑‍💻 Example 1: Quick Python Probe

import requests
BASE = "https://target.com"
endpoints = [
    "/api/internal/users",
    "/api/admin/config",
    "/api/dev/test"
]
for ep in endpoints:
    url = BASE + ep
    r = requests.get(url)
    print(f"{r.status_code} - {url}")

If you get:

200 - https://target.com/api/admin/config

You've just found a live hidden endpoint 😈

⚡ Example 2: Directory Fuzzing

For brute-forcing hidden APIs, I love ffuf.

ffuf -u https://target.com/api/FUZZ -w /usr/share/seclists/Discovery/Web-Content/api.txt -mc 200,301,302

It'll try hundreds of possible routes and tell you which ones exist. Just remember: don't go wild — always stay in-scope and respect rate limits. ❤️‍🔥

🧰 My Go-To Tools 🧠

None

💣 Real-World Example: How I Found a Hidden Admin API

During one of my bug bounty hunts, I noticed a JavaScript file referencing:

/api/internal/exportData

Curious, I sent a GET request — it responded with:

401 Unauthorized

Classic. But then I added an Authorization header copied from a normal user request, and boom 💥 — I got a JSON response with admin-only data exports.

That single hidden endpoint turned into a high-severity bug worth $$$.

Lesson: Never ignore what JS whispers to you.

🧑‍⚖️ Stay Ethical (Seriously!)

Always:

  • Stay within scope of your bug bounty or engagement.
  • Never exploit beyond proof-of-concept.
  • Avoid hitting live customer data.
  • And report responsibly.

Security research ≠ destruction — it's protection through discovery. 🛡️

🧩 Advanced Trick: GraphQL Introspection

Some modern apps use GraphQL APIs — and if introspection is enabled, it's like reading their entire API manual.

Try this:

curl -X POST https://target.com/graphql \
  -H "Content-Type: application/json" \
  -d '{"query":"{ __schema { types { name fields { name } } } }"}'

If you get a response full of queries and mutations — jackpot 🎯 You just discovered the entire schema.

🔍 2. How Hackers Discover Them

Let's walk through the process step-by-step 👇

🔸 a. Using Browser DevTools

Open your target website → Inspect → Network tab → Filter fetch/XHR. You'll often find requests like:

https://target.com/api/v1/config
https://target.com/api/private/featureflag

These aren't visible anywhere in the UI… but they exist. Boom 💥 — you just found a hidden endpoint.

🔸 b. Using Burp Suite + Wordlists

Use Burp Intruder or ffuf with API-specific wordlists.

Example:

ffuf -u https://target.com/api/FUZZ -w ~/wordlists/api.txt -mc 200,403

Try wordlists like: 👉 SecLists API Endpoints 👉 API Fuzz Wordlist (My GitHub)

🔸 c. Leaking Endpoints via JavaScript

Run this one-liner to find API URLs hidden in JS files:

grep -oP '(https?:\/\/[^\s"']+\/api\/[^\s"']+)' *.js

Tools like LinkFinder or JSParser automate this beautifully. 💻

🧠 3. Why Developers Hide Them (And Why You Should Care)

Developers sometimes leave these routes in production because:

  • "They're for internal use only."
  • "We'll remove it later." (They never do. 😅)
  • "Nobody will find them."

Guess what? Hackers always find them. Hidden APIs can expose:

  • Sensitive user data
  • Authentication flaws
  • Forgotten admin panels
  • Cloud configurations ☁️

🚨 4. Real-World Example: How a $2,000 Bug Was Found

A researcher once discovered an endpoint /api/v2/users/exportAll that exported every user email in CSV. No auth, no rate limit. He submitted it via a bug bounty program → $2,000 reward. 💰

This is why recon is everything — the more endpoints you find, the higher your chances.

💡 5. Bonus: Automate Hidden API Discovery

Let's make it easy using Python 👇

import requests
base_url = "https://target.com/api/"
endpoints = ["admin", "v1/users", "private/config", "dev/test"]
for ep in endpoints:
    url = base_url + ep
    r = requests.get(url)
    if r.status_code in [200, 403]:
        print(f"[+] Found endpoint: {url} ({r.status_code})")

You can find the full script here →

🚀 Want to Level Up Your Recon Game?

If you want a full, hands-on recon playbook — step-by-step with tools, scripts, wordlists, worksheets and real examples — grab my detailed recon guide for hackers and bug hunters here: Hackers' Recon Guide (detailed, practical, downloadable) → https://thehackerslog.gumroad.com/l/hackersreconguide

Check it out for walkthroughs, lab exercises, and everything I use to find high-value targets.

📚 Related Reads (From My Blog Series)

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The Secret Life of Subdomains 🌐: From Takeover to $$$ Bounties

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📌 Connect With The Hacker's Log

If you enjoyed this guide, join our growing ethical hacking community for advanced tutorials, case studies, and recon challenges!

🌐 Website: https://thehackerslog.com/ 📰 Substack: https://thehackerslog.substack.com/ 🛒R Recon Guide: https://thehackerslog.gumroad.com/l/hackersreconguide ✍️ Medium: https://medium.com/@vipulsonule71 🔗R LinkedIn: The Hacker's Log

Happy Hunting — and always, hack ethically. ⚔️