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Introduction:
In the high-stakes world of cybersecurity, companies are increasingly adopting a “hero’s welcome” approach for those who can break their systems. Bug bounty programs have emerged as a critical component of modern AppSec, turning the adversarial relationship on its head by financially rewarding ethical hackers for finding vulnerabilities before malicious actors do. Unlike automated scanners that look for low-hanging fruit, human ingenuity focuses on exploiting business logic flaws—bypassing restrictions to view unauthorized documents, escalate privileges, or manipulate prices—proving that the most severe bugs often lie in the functionality, not just the code.
Learning Objectives:
- Understand the core difference between automated scanning and manual business logic testing.
- Learn how to approach a target to identify privilege escalation and Insecure Direct Object References (IDOR).
- Gain practical skills in using common tools and commands to intercept traffic and manipulate requests for bug bounty hunting.
You Should Know:
1. The Mindset Shift: Beyond the Scanner
Most novice hunters make the mistake of running a vulnerability scanner (like Nessus or OpenVAS) and waiting for a report. As highlighted by top earners like Gal Nagli, this approach rarely yields critical findings. Scanners are designed to find known, signature-based flaws (like outdated versions). They cannot understand that an application allows you to view `Order ID: 12345` just by changing the URL to Order ID: 12346.
To think like a hunter, you must adopt a narrative: “If I were a malicious user, how would I abuse this feature?” This involves deep-diving into the application’s logic—signup flows, password reset mechanisms, and multi-step transactions.
2. Exploiting IDOR: Viewing Other People’s Data (Step-by-Step)
Insecure Direct Object References (IDOR) are among the most common and rewarding bugs. They occur when an application exposes a reference to an internal object (like a file or database key) without proper authorization checks.
Step‑by‑step guide (Linux/macOS using `curl` and Browser DevTools):
- Intercept the Request: Open your browser’s Developer Tools (F12) and go to the Network tab.
- Trigger the Action: Click on your profile or an invoice. Look for a request containing a numerical ID, UUID, or filename (e.g.,
https://example.com/download?invoice=1001`).curl`):
<h2 style="color: yellow;">3. Modify and Resend (usingRight-click the request in the Network tab and select “Copy as cURL”. Paste it into your terminal.
Modify the identifier and resend.
Original request (copy as cURL and modify the ID) Let's assume the original command is long. You extract the URL and Cookie. Attempt to access invoice belonging to another user (ID 1005) curl -X GET "https://example.com/download?invoice=1005" \ -H "Cookie: session=YOUR_SESSION_COOKIE" \ -H "User-Agent: Mozilla/5.0"
4. Analyze Output: If the server returns the invoice data for user `1005` without asking for re-authentication, you have found an IDOR. This bypasses the need for a password to access someone else’s documents.
3. Privilege Escalation: Becoming the Admin
Often, applications handle role-based access control (RBAC) on the front end. A low-privileged user might see “Edit Profile,” while an admin sees “User Management.” However, if the backend doesn’t validate the role for every request, a standard user can forcibly browse to admin functions.
Step‑by‑step guide (Using Burp Suite):
- Map the Application: Log in as an admin user and identify a sensitive function (e.g., `https://example.com/admin/deleteUser`). Log this request.
2. Switch Context: Log in as a standard user on a different browser or incognito session.3. Replay the Request:
– In Burp Suite, go to the Repeater tab.
– Paste the admin request (the exact URL and method).
– Replace the admin session cookie with the standard user’s session cookie.
– Send the request.
4. Check the Response: If the server responds with `200 OK` or a success message, the application failed to verify the user’s role on the backend, allowing a standard user to perform admin actions. -
Business Logic Abuse: Paying Less Than You Should
This is a favorite among hunters because it targets the core financial model of the application. It involves manipulating the flow of a transaction.
Step‑by‑step guide (API Security Testing):
- Initiate a Purchase: Add an item to your cart and proceed to checkout.
- Intercept the Final Request: Use Burp Suite to capture the `POST` request sent to the server when you click “Confirm Order” or “Apply Coupon.”
- Manipulate Parameters: Look for hidden parameters like
price,total,discount,currency, orquantity. Change them.
– Example: If the request contains {"item_id": "123", "price": 100, "quantity": 1}, change it to {"item_id": "123", "price": 1, "quantity": 1}.
4. Forward the Request: Allow the request to continue.
5. Verify: Check if the order confirmation page reflects the manipulated price. If the backend trusts the client-side price, you have just exploited a critical logic flaw.
5. Authentication Bypass: Getting In Without a Password
Forgetting passwords is human; implementing recovery insecurely is a bug. Attackers often target the “Forgot Password” or “Remember Me” functionality.
Step‑by‑step guide (Token Analysis):
- Request a Password Reset: For your own account.
- Inspect the Reset Link: Often, you receive an email with a link like: `https://example.com/reset?token=MjAyMy0xMC0yMHxqb2huZG9l`.
- Decode the Token: This token looks like Base64. Decode it in Linux:
Decode the token echo "MjAyMy0xMC0yMHxqb2huZG9l" | base64 --decode Output might be: 2023-10-20|johndoe
- Analyze: If the token is simply a concatenation of a timestamp and the username, it is predictable. Generate a token for a target user (e.g.,
2023-10-20|admin), encode it back to Base64, and manually visit the reset link.Encode a crafted token echo -n "2023-10-20|admin" | base64
- Result: If the application accepts this crafted token, you can change the admin’s password without ever knowing their original credentials.
What Undercode Say:
- Key Takeaway 1: Automation has a ceiling. The most lucrative vulnerabilities are found by understanding the application’s intended purpose and then subverting it. Business logic flaws (IDOR, price manipulation) consistently outperform technical vulnerabilities (XSS, SQLi) in impact and reward.
- Key Takeaway 2: Tool proficiency is mandatory, but tool dependency is a trap. Using `curl` for manual requests or Burp Suite for replay attacks is essential, but they are merely extensions of the hacker’s reasoning. The real skill lies in asking “what if?” during every step of the user journey.
The recent Wiz masterclass release underscores a vital truth in cloud and web security: the human element remains the most effective vulnerability scanner. As applications grow more complex, the ability to chain minor logical flaws into a critical exploit pathway becomes a superpower. For defenders, this means rigorous state management and server-side validation are non-negotiable. For hunters, it reinforces that patience and curiosity pay dividends far beyond what any automated tool can scrape from the surface.
Prediction:
As AI begins to write more backend code, we will likely see a surge in predictable logic flaws rather than memory corruption bugs. AI models trained on standard patterns may replicate insecure design patterns (like trust in client-side prices or predictable token generation) at scale. Consequently, the next wave of elite bug bounty hunters will pivot from pure code analysis to “AI behavior auditing”—probing the business logic that AI-generated code inadvertently hardcodes.
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Reported By: Gurban V – Hackers Feeds
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