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Introduction:
In-Direct Object Reference (IDOR) vulnerabilities remain a pervasive and high-impact flaw in modern web applications, allowing attackers to bypass authorization and access unauthorized data. A recent real-world case, where a detailed IDOR report secured a bug bounty over a prior submission, underscores the critical importance of meticulous documentation and exploitation technique. This article deconstructs the IDOR vulnerability, providing the technical commands and methodologies to identify, exploit, and ultimately report these flaws with the precision that bounty programs demand.
Learning Objectives:
- Understand the core mechanisms behind In-Direct Object Reference (IDOR) vulnerabilities.
- Master the manual and automated techniques for enumerating and testing object references.
- Learn how to craft a high-quality, actionable bug bounty report that stands out to security teams.
You Should Know:
- Enumerating Sequential Object IDs with curl and Bash
Verified Command List:
`curl -s “https://target.com/api/user/1” | jq`
`for id in {1..100}; do curl -s “https://target.com/api/user/$id” -o “user_$id.json”; done`
`seq 1 100 | xargs -I{} curl -s “https://target.com/api/v1/order/{}” -H “Authorization: Bearer $TOKEN”`
Step‑by‑step guide:
The first step in hunting for IDORs is identifying the parameters that control object access. These are often id, user_id, uid, order_id, etc. Use a tool like `curl` to manually test if changing the value of this parameter returns a different object. To automate testing against a range of sequential IDs, a simple Bash `for` loop or `xargs` command is incredibly effective. The `jq` command is used to parse and prettify JSON responses for easy analysis. Always ensure your requests include any necessary session cookies or authorization headers, which can be captured from your browser’s developer tools.
2. Burp Suite Intruder for Automated IDOR Testing
Verified Configuration:
- Attack Type: Sniper
- Payload Type: Numbers (sequential or from a custom list)
- Payload Settings: Define the range (e.g., from 1 to 10000, step 1).
Step‑by‑step guide:
While Bash scripts work, Burp Suite’s Intruder is the professional’s choice for robust testing. After browsing the target application normally, find a request that fetches an object (e.g., GET /api/customer/12345/details). Send this request to Burp Intruder. Highlight the object ID (e.g., 12345) and mark it as the payload position. In the Payloads tab, select the “Numbers” payload type. Configure a wide range (e.g., 1 to 10000) to test for sequential IDs. For non-sequential IDs, use a “Runtime file” payload with a wordlist of known IDs. Start the attack and analyze the responses for differing HTTP status codes (200 vs. 403/404) and varying response lengths, which indicate potential unauthorized access.
3. Identifying UUIDs and Non-Sequential References
Verified Command List:
`grep -roE ‘[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}’ /path/to/burp/logs/`
`cat response.js | python3 -c “import sys, json; print(json.load(sys.stdin)[‘user’][‘uuid’])”`
Step‑by‑step guide:
Not all applications use simple integers. Modern apps often use Universally Unique Identifiers (UUIDs). To find these, you must first gather a corpus of data by proxying your traffic through Burp Suite and browsing all application functionality. Then, use `grep` with a regular expression designed to match the UUID format to scan your Burp project file or logs. Alternatively, review responses in Burp’s Logger or Repeater tabs manually. Once you have a list of potential UUIDs, you can test them in other user contexts using the same `curl` or Burp Intruder techniques, using the “Runtime file” payload type to load your list of found UUIDs.
4. Testing Horizontal and Vertical Privilege Escalation
Verified Command Snippet:
`curl -s -X GET “https://target.com/api/admin/users” -H “Cookie: session=user_cookie”`
`curl -s -X GET “https://target.com/api/admin/users” -H “Cookie: session=admin_cookie”`
`curl -s -X POST “https://target.com/api/user/567/delete” -H “Authorization: Basic dXNlcjpwYXNz”`
Step‑by‑step guide:
An IDOR isn’t just about accessing another user’s data (horizontal privilege escalation); it can also be about performing actions as a privileged user (vertical privilege escalation). Test every HTTP method (GET, POST, PUT, DELETE, PATCH). For example, if a regular user can view their own profile at GET /api/users/[bash], try changing the method to `DELETE` on the same endpoint. To test for vertical escalation, capture a request from a low-privilege user that performs an action (e.g., modifying their profile). Then, try replaying that exact request while authenticated as a different low-privilege user (horizontal). Finally, try replaying it while authenticated as an admin user (vertical) to see if the action is permitted on a lower-privileged account.
5. Leveraging API Documentation for Hidden Endpoints
Verified Command List:
`curl -s https://target.com/robots.txt | grep -i disallow`
`curl -s https://target.com/api/v1/swagger.json | jq ‘.paths’`
`nmap -p 443 –script http-jsonp-detection target.com`
Step‑by‑step guide:
Often, the API endpoints vulnerable to IDOR are not immediately visible in the main user interface. Discovering these hidden endpoints is half the battle. Start by checking common files like /robots.txt, /sitemap.xml, and /api-docs. Many modern applications use OpenAPI/Swagger documentation; check for files like /swagger.json, /openapi.json, or /api-docs. Use `curl` to fetch these and `jq` to parse the JSON to extract all available API paths. Tools like `nmap` with the `http-jsonp-detection` script can also help. Each discovered endpoint represents a new attack surface for IDOR testing.
6. Crafting the Perfect IDOR Bug Bounty Report
Verified Template:
IDOR allowing unauthorized access to [Sensitive Data] via [Parameter Name] in [bash]
Vulnerability Type: In-Direct Object Reference (IDOR)
Severity: [e.g., Medium/High]
Endpoint: `https://victim.com/api/v1/user/[bash]`
Steps to Reproduce:
1. Log in as user A (email:[email protected]).
2. Capture the request `GET /api/v1/user/101` (your own ID).
3. Change the `id` parameter to `102` (another user’s ID) and replay the request.
4. Observe the HTTP 200 response containing user B’s full profile data (PII).
Proof of Concept: [Attach screenshots of Burp/curl requests/responses]
Impact: Any authenticated user can access the sensitive personal information of any other user.
Step‑by‑step guide:
A winning report is clear, concise, and leaves no room for doubt. The title must immediately convey the flaw and its impact. The steps to reproduce must be a numbered list that the triager can follow exactly, using provided test accounts if necessary. The proof of concept is critical: include annotated screenshots of your Burp Suite repeater window or the full `curl` command and its output, highlighting the modified parameter and the sensitive data in the response. Explicitly state the impact on the application’s confidentiality, integrity, or availability.
What Undercode Say:
- The value of a bug bounty report is not just in finding the bug, but in proving its impact with crystal-clear evidence.
- Automation is key for discovery, but manual analysis is required to understand context and maximize severity.
The case of Mohamed Amgad’s successful IDOR report is a masterclass in professional bug hunting. It wasn’t the initial discovery that won the bounty, but the superior quality of the report. This highlights a critical shift in the bounty ecosystem: volume is being superseded by value. Programs are inundated with low-quality, duplicate submissions. The researchers who thrive are those who act not just as finders, but as consultants, providing the developer team with an unambiguous roadmap to the flaw and its consequences. This elevates the practice from a technical scavenger hunt to a true security partnership, ultimately leading to more secure applications for everyone.
Prediction:
The automation of vulnerability discovery will continue to accelerate, leading to an even higher volume of low-effort, duplicate submissions. This will cause bounty programs to further prioritize report quality, context, and exploit chain sophistication when determining rewards. Researchers who combine automated testing with manual exploitation techniques and, crucially, expert-level communication skills will see their earnings significantly outpace those who rely on tooling alone. The “gold rush” era of easy bugs is closing, ushering in a new era of professional vulnerability research.
🎯Let’s Practice For Free:
IT/Security Reporter URL:
Reported By: Mohamed Amgad – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
