The IDOR Goldmine: How One Hunter Bagged 7 Critical Vulnerabilities in a Single Month

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Introduction:

In the shadowy corridors of web application security, Insecure Direct Object References (IDOR) remain a reigning champion of critical vulnerabilities, often leading to massive data breaches. By focusing exclusively on this bug class, a dedicated researcher demonstrated that systematic methodology and deep understanding can turn a common flaw into a consistent payout, uncovering 7 distinct IDORs in one targeted program. This case study deconstructs the hunter’s mindset into actionable techniques you can implement immediately.

Learning Objectives:

  • Understand the core principles of IDOR vulnerabilities and how to systematically hunt for them.
  • Learn practical, hands-on techniques for parameter manipulation, state alteration, and endpoint testing.
  • Develop a methodology for automating reconnaissance and validating potential IDOR findings.

You Should Know:

1. Reconnaissance and Endpoint Mapping: The Foundation

Before testing, you must map the application’s object structure. This involves identifying every API endpoint that handles object identifiers (e.g., user IDs, order numbers, document UUIDs).

Step‑by‑step guide:

Intercept Traffic: Use Burp Suite or OWASP ZAP to proxy your browser traffic. Log into the application and navigate through all functionalities.
Target Identification: In your proxy history, look for endpoints containing predictable parameters like user_id=12345, account=6789, or uuid=abc123-def456. Focus on GET, POST, PUT, and `DELETE` requests.
Pattern Analysis: Note the pattern of these IDs. Are they sequential? Are they UUIDs? This informs your attack strategy. Use tools like `grep` to filter logs:

 In Burp, save project logs and analyze
cat request_log.txt | grep -E "(id=|user=|account=)" | less

2. Basic Parameter Manipulation: The First Test

The simplest test is changing the ID parameter in a request to access another user’s data.

Step‑by‑step guide:

  1. Find a request that fetches your data, e.g., GET /api/v1/users/12345/profile.
  2. Using Burp Repeater or a browser extension, change `12345` to 12346.
  3. Send the request. If it returns another user’s profile data, you have a classic IDOR.

4. Linux Command Line Test with `curl`:

 Your authorized request
curl -H "Authorization: Bearer YOUR_TOKEN" https://api.target.com/v1/users/12345/profile
 The IDOR test
curl -H "Authorization: Bearer YOUR_TOKEN" https://api.target.com/v1/users/12346/profile

Compare the outputs.

3. Testing State-Changing Requests (POST/PUT/DELETE)

IDOR is not just about viewing data; it’s about performing actions on unauthorized objects. This is often more severe.

Step‑by‑step guide:

  1. Find a request that updates, creates, or deletes an object tied to an ID (e.g., `POST /api/updateShippingAddress` with a body of {"address_id": "555"}).
  2. In Burp Repeater, change the `address_id` to one belonging to a different user.
  3. Send the request and check the response. A `200 OK` or success message often indicates the state change was applied to the wrong object.
  4. Verify by performing a subsequent `GET` request to see if the change persisted for the victim’s object.

4. Exploring Horizontal to Vertical Privilege Escalation

Sometimes an IDOR that lets you access another user’s data (horizontal escalation) can be leveraged to access admin data (vertical escalation) if ID patterns are predictable.

Step‑by‑step guide:

  1. Confirm a horizontal IDOR (e.g., accessing `user_id=100` and user_id=101).
  2. Enumerate low-numbered IDs, which are often reserved for system administrators during initial seeding. Use `curl` in a loop: 
    for i in {1..10}; do
echo "Testing ID: $i"
curl -s -H "Authorization: Bearer YOUR_TOKEN" https://api.target.com/v1/users/$i/profile | grep -i "admin|email"
done
  3. Analyze responses for differences in data structures or privileged information.

5. Bypassing UUIDs and Hashed IDs

Applications often use UUIDs or hashed IDs to avoid predictability. However, these can still be vulnerable if the application doesn’t validate ownership.

Step‑by‑step guide:

  1. If you see an endpoint like /invoice/abc123def456, don’t assume it’s safe. Find where these IDs are leaked.
  2. Check other application responses. Your profile page (/api/me) might return an array of your invoice IDs. Try using one of your IDs to access another user’s resource at a different endpoint.
  3. Test for Referential IDOR: An endpoint might use a UUID in the path but a numeric ID in the body. Try replacing the body ID while keeping the path UUID. 
    Request: PUT /api/invoices/550e8400-e29b-41d4-a716-446655440000
Body: {"invoice_id": 78912, "amount": 100} <-- Change 78912 to another number.

6. Automating Discovery with Fuzzing

Manual testing is powerful, but automation can help find obscure parameters.

Step‑by‑step guide using Burp Intruder:

  1. Right-click a request with an object ID and “Send to Intruder.”
  2. In the Positions tab, clear payload positions and highlight only the ID value (e.g., 12345). Mark it as a payload position.
  3. Go to the Payloads tab. For numeric IDs, use a “Numbers” payload type to iterate through a range (e.g., 12340 to 12350). For leaked lists of IDs, use a “Simple List” payload.
  4. In the Settings tab, add a “Grep – Extract” rule to pull unique data (like email addresses) from responses.
  5. Start the attack. Review results for HTTP status codes `200` where the extracted data differs from your own, indicating potential IDOR.

7. The Critical Validation Step: Confirming Impact

A successful IDOR test in your toolkit doesn’t prove impact. You must demonstrate what an attacker could do.

Step‑by‑step guide:

  1. Document the Flow: Show the unauthorized request and the sensitive data returned (obfuscate personally identifiable information (PII)).
  2. Proof of Concept (PoC): Write a simple script that performs the attack, or provide a cURL command the triager can run.
  3. Argue the Impact: Can it leak PII? Can it modify financial data? Can it delete critical resources? Link the finding to a specific business risk.

What Undercode Say:

  • Persistence Over Genius: This case proves that focused, persistent hunting on a single vulnerability class is more effective than sporadic, broad testing. Mastery of IDOR logic unlocks multiple findings.
  • Methodology is Key: The hunter’s success wasn’t luck; it was a repeatable process of map, test, manipulate, and escalate. Building a personal methodology is crucial for consistent results in bug bounty programs.

The systematic approach outlined—moving from reconnaissance to exploitation to impact validation—transforms IDOR hunting from a guessing game into a engineering discipline. By treating the application as a structured data system with flawed access controls, a hunter can efficiently uncover logical weaknesses that automated scanners will almost always miss.

Prediction:

The prevalence of IDOR vulnerabilities will persist despite advances in secure frameworks, as developers continue to incorrectly assume that obfuscated identifiers (UUIDs) equate to authorization. The next frontier will see a rise in “mass assignment” IDORs in GraphQL and gRPC APIs, where object references are nested deep within complex queries. Furthermore, the integration of AI-generated code without proper security context will inadvertently introduce novel IDOR patterns, making deep, logical understanding of application flow more valuable than ever for both attackers and defenders.

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IT/Security Reporter URL:

Reported By: Abdalkreem Dagga – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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