Posted by JavaScript files (JS) are an essential part of modern web applications, powering everything from user interactions to API requests. However, developers often overlook the security risks associated with leaving sensitive information in JS files. This information can be even more valuable when looking at previous versions of these files stored on the Wayback Machine (Internet Archive).
By analyzing archived JavaScript files, security researchers, bug bounty hunters, and penetration testers can uncover deprecated API endpoints, hidden features, input parameters, and even hardcoded credentials. In this blog, we’ll explore how to retrieve, analyze, and extract valuable data from old JS files and additional methods to enhance this approach.
Why Should You Look at Archived JavaScript Files?
Archived JS files can provide a goldmine of information for security testing and reconnaissance. Here’s what you might uncover:
1. Deprecated API Endpoints
- Older JS files often reference API endpoints that have been removed from newer versions of an application.
- These endpoints may still be accessible and vulnerable to IDOR (Insecure Direct Object References), SQL injection, or other attacks.
- Example:
/api/v1/users/deletemight still exist even if it’s not in the latest JS file.
2. Hidden Features & Components
- Developers frequently include references to beta features or admin functionality in their JS files.
- These hidden components may still be accessible even if they are no longer public.
- Example: A hidden admin panel URL that isn’t linked anywhere on the site but is referenced in an older JS file.
3. Input Parameters & API Keys
- JavaScript files often contain query parameters, API tokens, or authentication mechanisms.
- These details can help reconstruct API requests for further testing.
- Example:
fetch('https://api.example.com/data?key=12345')
4. Hardcoded Credentials
- Some developers accidentally hardcode usernames, passwords, or API keys in JavaScript files.
- Even if these credentials were later removed, older versions may still contain valid secrets.
- Example:
const authKey = "hardcoded-password123";
How to Retrieve Archived JavaScript Files
The Wayback Machine stores historical snapshots of web pages, including JavaScript files. Here’s how you can find them:
Step 1: Identify the Target Website
- Find JavaScript files by opening the Developer Tools (F12) → Network → JS in your browser.
- Look for externally hosted JavaScript files (e.g.,
https://example.com/js/main.js).
Step 2: Search for Archived Versions
Use the Wayback Machine to check previous versions:
curl -s "https://web.archive.org/cdx/search/cdx?url=https://example.com/js/main.js&output=text&fl=original,timestamp"
Or, manually check via:
- Visit: https://web.archive.org
- Enter the URL of the JavaScript file
- Browse different snapshots and compare versions
Step 3: Analyze the JavaScript File
- Download the archived versions of the JS file.
- Use tools like grep, jq, or Burp Suite to search for API keys, endpoints, or credentials:
grep -E "api|key|token|secret|password" old_script.js
Step 4: Compare Versions
Use diff or any code comparison tool to find changes between versions:
diff old_script.js new_script.js
- Look for removed API endpoints, changed keys, or hidden parameters.
Additional Techniques for Finding Exposed Information
1. Google Dorking for JavaScript Files
Google can help you find public JavaScript files that are indexed:
site:example.com filetype:js
You can also look for API keys in repositories:
site:github.com "apikey="
2. Checking CDN Caches
Some websites host JS files on CDN (Content Delivery Network) services like Cloudflare or Akamai. These might still contain old versions:
https://cdn.example.com/js/main.js- Use
curl -Ito check for cache headers.
3. Searching in Public Repositories
Developers often upload JavaScript files to GitHub, GitLab, or Bitbucket:
- Search for exposed credentials in repositories:
git clone https://github.com/example/repo.git
cd repo
grep -r "api_key" .
4. Using JS Beautifiers for Minified Files
Some JS files are minified to make analysis harder. Use:
js-beautify script.min.js -o script.js
Then manually inspect the beautified file.
Real-World Examples of JavaScript Reconnaissance
Case 1: Leaked Admin Panel in an Older JS File
- A pentester found a reference to
/admin/loginin an archived JavaScript file. - The panel was still accessible, and the default credentials worked.
Case 2: Hardcoded API Keys Exposed
- An older version of
config.jscontained an API key for a payment gateway. - This key allowed unauthorized transactions.
Case 3: Hidden Feature in a SaaS Application
- A JS file referenced an undocumented beta feature (
/feature-beta). - The feature allowed access to sensitive user data.
Mitigation: How Developers Can Secure JavaScript Files
While security researchers can use these techniques for ethical hacking, developers should be aware of how to prevent such leaks:
1. Avoid Hardcoding Secrets in JS Files
- Use environment variables instead of embedding API keys.
- Example: Store secrets in
.envfiles and fetch them securely.
2. Regularly Audit and Rotate API Keys
- Rotate and expire old API keys frequently.
- Use least privilege access for API tokens.
3. Obfuscate JavaScript Code (With Caution)
- While obfuscation makes analysis harder, it’s not foolproof.
- Example tools: UglifyJS, Obfuscator.io
4. Monitor Public Archives & Repositories
- Set up alerts for leaks using tools like GitHub Secret Scanning, LeakIX, or Shodan.
Conclusion
JavaScript reconnaissance via the Wayback Machine is an invaluable technique for security researchers, allowing them to uncover hidden endpoints, deprecated features, hardcoded secrets, and API parameters. By leveraging tools like curl, diff, grep, and Google Dorking, you can extract valuable information from historical JavaScript files.
At the same time, developers must take proactive measures to secure their JavaScript files and prevent sensitive data from being exposed.
💡 Have you found an interesting JavaScript file using this method? Share your findings in the comments!
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