How I Turned a Dark Web Sketch into a $ Bug Bounty Payday 🕵️‍♂️💸

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You know that feeling when you're scrolling through random stuff online, half-asleep, and you stumble upon something so bizarre it jolts you awake? For me, it wasn't a cat video. It was a leaked API endpoint buried in a dark web forum rant. It was like finding a secret recipe for chaos in a villain's kitchen, and I, the friendly neighborhood white hat, decided to bake my own bounty cake. 🍰

Act 1: The Digital Dumpster Dive 🗑️

It all started during my weekly "grimace-and-browse" session on a certain Tor-based cybercrime forum. I wasn't looking for anything specific, just monitoring the chatter about new exploits and data leaks. My eyes glazed over until I saw a post from a disgruntled "developer" complaining about his former employer, a major fintech company we'll call "SecureBank Inc."

In his rant, he pasted what he claimed was "useless junk" from their internal debugging logs. Most people scrolled past. But my spidey-senses tingled. Buried in that code vomit was a goldmine:

# From the leaked log snippet:
[DEBUG] Request ID: a1b2c3d4 | Endpoint: `https://api.internal.securebank.com/v3/admin/user_data/export?format=json&token=[REDACTED]`
[ERROR] Authentication failed for token: eyJhbGc... [a long JWT token snippet]

Bingo. An internal admin endpoint and a partial JWT token. This wasn't a simple ?id=1 parameter; this was a direct backdoor to the kingdom's data vault. The criminal saw it as garbage. I saw it as a treasure map.

Act 2: From Leaked Token to Broken Authorization 🔓

The first step was confirmation. I couldn't use the leaked token directly — it was invalid and using it would be unethical. But I now knew the structure of the API call.

I started with standard reconnaissance on the main securebank.com domain. Using a combination of amass and subfinder, I built a massive list of subdomains.

subfinder -d securebank.com -silent | tee subdomains.txt
amass enum -passive -d securebank.com | tee -a subdomains.txt

Then, I used httpx to find live hosts and filter for specific keywords.

cat subdomains.txt | httpx -silent | grep -E "(api|internal|admin)" | tee live_endpoints.txt

And there it was, staring back at me: https://api.internal.securebank.com

My heart raced. The endpoint from the leak was real and accessible from the outside internet! This was a massive misconfiguration in itself.

Act 3: The Art of Token Manipulation & The IDOR Heist 🎭

Now for the authorization bypass. The leaked log showed they used JWT (JSON Web Tokens) for authentication. I created a free account on SecureBank's main application and captured a valid, low-privilege JWT token using Burp Suite.

A standard JWT looks like this: header.payload.signature

I used jwt_tool to analyze my token:

python3 jwt_tool.py eyJhbGc... [my_low_privilege_token]

The payload revealed:

{
  "username": "my_user",
  "role": "customer",
  "iss": "securebank-auth",
  "iat": 1648812345,
  "exp": 1648815945
}

The key was the "role": "customer". I needed to become an "admin". But simply changing the role wouldn't work; the token is cryptographically signed. Without the secret key, I couldn't forge a valid one.

This is where the real magic happened. I recalled a technique often discussed in advanced application security circles: JWT Algorithm Confusion.

I noticed the token header used the HS256 algorithm (HMAC + SHA-256). This algorithm uses a single secret key to both create and verify the signature. Sometimes, if the server is misconfigured, it will use a public key (like from an RSA pair) as the HMAC secret. If the public key is discoverable, you can use it to sign your own tokens.

My mission was to find that public key. I fired up curl and tried common endpoints:

curl -s https://api.securebank.com/.well-known/jwks.json | jq
# No response.
curl -s https://auth.securebank.com/.well-known/jwks.json | jq
# BINGO!

The server returned a JSON Web Key Set (JWKS). I grabbed the public key (kty, n, e values) and used jwt_tool to forge a new token.

python3 jwt_tool.py eyJhbGc... [my_token] -T -pk public_key.pem

jwt_tool now re-signed my token using the public key as the HMAC secret. I changed the payload to "role": "super_admin" and generated a new, validly signed token.

Act 4: The Payload & The Grand Prize 🏆

With my forged admin JWT, it was time to call the leaked endpoint. My hands were literally shaking.

The Payload:

GET /v3/admin/user_data/export?format=json HTTP/1.1
Host: api.internal.securebank.com
Authorization: Bearer eyJhbGc... [my_forged_admin_token]
User-Agent: Mozilla/5.0

I sent the request in Burp Repeater…

The Response:

HTTP/1.1 200 OK
Content-Type: application/json
[
  {
    "user_id": 1,
    "email": "admin@securebank.com",
    "ssn": "123-45-6789",
    "tax_id": "98-7654321",
    "address": "123 Main St...",
    "portfolio_value": 450000
  },
  // ... thousands of user records ...
]

Jackpot. 💥 I had just performed a successful Insecure Direct Object Reference (IDOR) combined with a JWT Confusion Attack, leading to a full Sensitive Data Disclosure of PII and financial information. I immediately stopped my testing and closed the connection.

The White Hat's Moral 🦸

The dark web isn't just a marketplace for criminals; it's a library of their mistakes. They leak, they brag, they complain. By learning their language and understanding their "playbooks," we can find the weak spots in our defenses before they do. This wasn't just about a parameter or a simple flaw. It was about connecting the dots between an opsec failure, a cryptographic misconfiguration, and an authorization bypass to tell a story that saved a company from a devastating breach.

So next time you hear about the dark web, don't just think of the shadows. Think of the treasure maps waiting for a white hat to read them. 🗺️

Proof of Concept (POC) Summary Table

StageTool/MethodKey FindingReconnaissancesubfinder, amass, httpxFound live api.internal.securebank.comToken Analysisjwt_toolIdentified JWT using HS256 algorithmKey DiscoverycurlFound public JWKS at auth.securebank.comExploitationJWT Algorithm ConfusionForged admin token & accessed data export endpointImpactIDOR + Data DisclosureExposed full user PII & financial records

This version maintains all the technical depth while being completely generic and using redacted names as requested! The story flows naturally while providing genuine educational value for the bug bounty community.

Connect with Me!

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• Instagram: @rev_shinchan
• Gmail: rev30102001@gmail.com

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#BugBounty, #CyberSecurity, #InfoSec, #Hacking, #WebSecurity, #CTF