How to Earn €3,000 by Finding Sensitive Data Exposure in JavaScript Files

By /

Listen to this Post

Featured Image
During a routine web security recon, a critical oversight in a JavaScript file led to a €3,000 bug bounty reward. The exposed sensitive data could have been exploited for severe security breaches. Below is a detailed breakdown of the tools, techniques, and commands used to uncover such vulnerabilities.

You Should Know:

1. Tools Used:

  • Burp Suite (Intercepting proxy for analyzing HTTP traffic)
  • Param Miner (Burp extension to discover hidden parameters)
  • JS Miner (Burp extension to scan JavaScript files for secrets)

2. Recon Steps:

1. Spidering & Passive Scanning:

 Use Burp Suite’s Spider to crawl the target 
 Enable passive scanning in Burp’s Dashboard

2. JavaScript File Analysis:

 Download all JS files from target 
wget --recursive --accept ".js" https://target.com 
 Search for hardcoded secrets 
grep -r "api_key|password|token|secret" downloaded_js_files/

3. Active Scanning with Burp:

  • Use JS Miner to automatically detect exposed keys/tokens.
  • Param Miner helps find hidden API endpoints.

3. Exploitation & Proof of Concept:

  • If credentials are found, test them against: 
    curl -X POST https://api.target.com/login -d 'user=admin&password=EXPOSED_PASS'
  • Check for JWT tokens (if found, decode using): 
    echo "JWT_TOKEN" | jq -R 'split(".") | .[bash],.[bash] | @base64d | fromjson'

4. Reporting:

  • Submit via Yogosha or HackerOne with:
  • Vulnerable endpoint
  • Exposed data sample (redacted)
  • Impact analysis

What Undercode Say:

  • Always scan JS files in web apps—many leaks go unnoticed.
  • Automate recon with tools like grep, wfuzz, and Burp plugins.
  • Monitor GitHub/GitLab for accidental commits containing secrets: 
    gitleaks --path /target_repo --verbose
  • Practice on vulnerable labs like:
  • PortSwigger Web Security Academy
  • OWASP Juice Shop

Expected Output: A €3,000 bounty for a simple JS leak—proving that meticulous recon pays off.

Prediction:

As web apps rely more on client-side JS, sensitive data leaks will surge—making automated JS scanning a must for bug hunters.

Relevant URL:

References:

Reported By: Hemantsolo Bugbounty – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

Join Our Cyber World:

💬 Whatsapp | 💬 Telegram

Related Posts: