From Recon to Reward: How Automated API Scanning Exposed a ,000 PII Leak

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Introduction:

In the high-stakes arena of bug bounty hunting, visibility is everything. A recent critical finding on a Bugcrowd program, which netted an estimated $3,000 bounty, underscores a fundamental truth: manual testing alone is no longer sufficient. The discovery hinged on the use of advanced reconnaissance toolkits to identify misconfigured API endpoints and exposed Basic Authentication credentials. This article breaks down the methodology behind such finds, providing a technical deep dive into the automated reconnaissance and credential discovery techniques that separate critical vulnerabilities from missed opportunities.

Learning Objectives:

• Understand how to build and utilize an automated reconnaissance pipeline for large-scale asset discovery.
• Learn techniques to identify and exploit misconfigured API endpoints and exposed Basic Authentication.
• Master the use of specific Linux and Windows tools for credential harvesting and information disclosure analysis.

You Should Know:

1. The Reconnaissance Pipeline: Automating Asset Discovery

The foundation of any successful bug bounty campaign is a robust reconnaissance phase. The goal is to expand your attack surface by discovering subdomains, hidden directories, and API endpoints that aren’t publicly linked. This involves chaining multiple open-source tools and wordlists.

Step‑by‑step guide for setting up a basic automated recon pipeline on Linux:
1. Subdomain Enumeration: Start with tools like `subfinder` and `assetfinder` to gather subdomains from various sources.

 Install subfinder (if not already installed)
go install -v github.com/projectdiscovery/subfinder/v2/cmd/subfinder@latest

Run subfinder against a target domain
subfinder -d target.com -o subdomains.txt

Use assetfinder for additional sources
assetfinder --subs-only target.com >> subdomains.txt

2. Resolving and Filtering: Use `httpx` to probe for live hosts and web servers from your list of subdomains. This filters out dead hosts and gives you a clean list of active targets.

 Install httpx
go install -v github.com/projectdiscovery/httpx/cmd/httpx@latest

Probe for live hosts and save the output
cat subdomains.txt | httpx -o live_hosts.txt

3. Port Scanning for Non-Web Services: Don’t ignore non-standard ports. Use `naabu` to find open ports that might be hosting APIs or admin panels.

 Install naabu
go install -v github.com/projectdiscovery/naabu/v2/cmd/naabu@latest

Scan live hosts for top 1000 ports
naabu -list live_hosts.txt -top-ports 1000 -o open_ports.txt

2. Hunting for Exposed API Endpoints and Documentation

Once you have a list of live hosts and open ports, the next step is to aggressively search for API-related paths. Developers often leave API documentation (like Swagger/OpenAPI) or unlinked endpoints exposed, which can reveal the entire structure of the backend.

Step‑by‑step guide for API endpoint discovery:

1. Directory and File Brute-forcing: Use `ffuf` or `gobuster` with specialized API wordlists to fuzz for common API paths.

   Using ffuf with a common API wordlist
   ffuf -u https://target.com/FUZZ -w /path/to/api/wordlist.txt -ac -c -v -o api_endpoints.json
   

2. Identifying API Documentation: Specifically look for paths like /swagger, /api/docs, /v1/api-docs, /openapi.json, or /graphql. Finding these can provide a roadmap for testing.
3. Analyzing JavaScript Files: Endpoints are often hardcoded in JavaScript files. Use tools like `getJS` or `LinkFinder` to extract URLs from JS files.

   Using getJS to grab all JS file links
   echo "https://target.com" | getJS --complete >> js_files.txt
   
   Then use LinkFinder to extract endpoints from each JS file
   python3 LinkFinder.py -i https://target.com/static/js/main.chunk.js -o cli
   

4. Credential Discovery: Finding the Keys to the Kingdom
   The original post mentioned “exposed Basic Authentication credentials.” These are often found in plaintext in configuration files, source code comments, or even public repositories. Automated scanning is crucial for detecting these slips at scale.

Step‑by‑step guide for credential hunting:

1. Searching for Configuration Files: Use `ffuf` to look for files that commonly contain credentials, such as .env, config.php, database.yml, or backup.sql.

   Fuzzing for sensitive files
   ffuf -u https://target.com/FUZZ -w /path/to/sensitive-files.txt -fc 403,404
   

2. Pattern Matching with grep: If you have access to a codebase (e.g., from an exposed `.git` folder or a misconfigured S3 bucket), use `grep` to search for credential patterns.

   Recursively search for password strings in downloaded code
   grep -r -i "password" .
   grep -r -E "(AWS|aws)<em>secret_access_key" .
   grep -r -E "api[</em>-]?key" .
   

3. Windows Command for Local Analysis: If you are analyzing a cloned repository on Windows, you can use PowerShell for similar pattern matching.

   Recursively search for common credential patterns
   Get-ChildItem -Recurse -File | Select-String -Pattern "(password|apikey|secret|token)" | Select-Object Filename, Line
   

4. Testing for PII Exposure in Misconfigured Endpoints

After discovering endpoints and potential credentials, the manual validation phase begins. The goal is to access these endpoints and verify if they return Personally Identifiable Information (PII) like emails, addresses, or financial data.

Step‑by‑step guide for testing discovered endpoints:

1. Manual Exploration with cURL: Use `cURL` to interact with the discovered endpoints. Test for excessive data exposure by accessing base endpoints.

   Attempt to access an API endpoint without any parameters
   curl -X GET https://target.com/api/v1/users -H "Authorization: Basic base64encodedcreds"
   
   Test for Insecure Direct Object References (IDOR) by incrementing IDs
   curl -X GET https://target.com/api/v1/users/1234
   

2. Intercepting with Burp Suite: Configure your browser to proxy traffic through Burp Suite. As you manually navigate the application, Burp will log all requests. Use the “Target” tab to analyze the site map and identify any API calls that return JSON data. Check the responses for PII.
3. Automating Response Analysis: Use `httpx` to filter responses based on content length or the presence of specific keywords indicative of PII (e.g., “ssn”, “email”, “credit_card”).

   Check for specific strings in the response body of live hosts
   cat live_hosts.txt | httpx -silent -mc 200 -ms "email"
   

5. Exploiting Basic Authentication Misconfigurations

Discovering Basic Authentication is just the first step. The real impact comes from misconfigurations like default credentials, weak password policies, or the authentication being applied over HTTP instead of HTTPS.

Step‑by‑step guide for exploiting Basic Auth:

1. Testing for Default Credentials: If the hostname suggests a known technology (e.g., `tomcat` or jenkins), test for default credentials (e.g., admin:admin, tomcat:tomcat).
2. Brute-forcing with hydra: If default credentials fail, a controlled brute-force attack might be permissible, but always check the program’s scope and rules of engagement first.

   Example using hydra to brute-force Basic Auth on a specific path
   hydra -L /usr/share/wordlists/usernames.txt -P /usr/share/wordlists/passwords.txt target.com http-get /admin
   

3. Checking for Transport Security: Verify if the Basic Authentication is transmitted over HTTPS. If the login page is available over HTTP, credentials are sent in plaintext, making them vulnerable to Man-in-the-Middle (MITM) attacks on the same network.

   Check if the site supports HTTPS and redirects from HTTP
   curl -I http://target.com/admin
   

What Undercode Say:

Key Takeaway 1: Automation is a Force Multiplier

The $3,000 bounty wasn’t found by accident. It was the direct result of a systematic, automated approach to reconnaissance. By casting a wide net with tools like subfinder, httpx, and ffuf, the researcher was able to uncover assets and misconfigurations invisible to standard browsing. This highlights that in modern bug bounty, success is less about genius and more about thorough, scalable methodology.

Key Takeaway 2: Visibility Extends Beyond the OWASP Top 10
While the finding involved a “Critical PII exposure,” the root cause was configuration management. Misconfigured APIs and exposed credentials are not new vulnerabilities but operational security failures. This serves as a critical reminder for developers and security teams: hardening configurations, removing default credentials, and ensuring documentation isn’t publicly accessible are as vital as patching code-level flaws. For the ethical hacker, this means that sometimes the most lucrative bugs are the simplest oversights.

Prediction:

As bug bounty programs become more competitive and organizations improve their patching of common web vulnerabilities, the next wave of critical findings will increasingly stem from complex, chained attacks discovered through automated recon. We will see a rise in “configuration complexity” bugs—where a combination of a misconfigured S3 bucket, an exposed API key, and a vulnerable endpoint leads to a massive data breach. This will push the demand for hunters who can not only run tools but also intelligently correlate disparate data points from automated scans to build high-impact exploit chains. The future of bug bounty belongs to the architects of automated reconnaissance pipelines.

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