How One Bug Bounty Appeal Overturned a Duplicate Ruling and Why Your Report’s Technical Precision Matters More Than the Finding Itself + Video

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Introduction:

In bug bounty programs, a “duplicate” classification often feels like a dead end—a definitive closure that rewards the first reporter and leaves subsequent finders empty-handed. But as security researcher MONSIF HMOURI recently demonstrated, a duplicate decision is not always the final word. By dissecting the affected method’s technical behavior, documenting the true impact, and clearly articulating the remediation scope, he successfully overturned a duplicate ruling, reopened the report as a P3 submission, and reinforced a critical lesson: finding the vulnerability is only half the battle—the other half is proving it with surgical precision.

Learning Objectives:

  • Master the technical and procedural steps for effectively appealing a duplicate bug bounty report.
  • Understand how to differentiate your IDOR or access control finding from prior submissions through behavioral analysis and evidence.
  • Learn how to document, test, and communicate access control vulnerabilities to maximize impact and acceptance.

You Should Know:

  1. Anatomy of a Duplicate Appeal: Technical Evidence That Moves the Needle

A duplicate classification in platforms like Bugcrowd or HackerOne typically means your finding overlaps with an already-submitted issue. However, duplicates are not always identical—they can differ in exploitability, attack surface, business impact, or remediation scope. Overturning one requires a technical appeal that goes beyond “I found it first.”

HMOURI’s approach centered on three pillars: technical behavior analysis, impact reassessment, and remediation scope clarification. Instead of simply restating the vulnerability, he examined how the affected endpoint behaved under different conditions—authorization headers, user roles, and object references—and demonstrated that his finding represented a distinct attack vector or a broader impact than the original report.

Step‑by‑step guide for building an appeal-ready technical dossier:

  1. Re‑test the endpoint under multiple contexts. Capture requests using Burp Suite or OWASP ZAP. Log in with different privilege levels (low, medium, high) and attempt to access the same object reference. Document every response.
  2. Compare your finding with the alleged duplicate. If the original report targeted GET /api/users/123, but your finding affects `POST /api/users/123/update` with the same IDOR, that’s a different method and potentially different impact.
  3. Quantify the business impact. Does your finding expose PII, financial data, or administrative functions? Use the CVSS scoring system to articulate severity.
  4. Draft a concise, evidence‑backed appeal. Reference the original ticket number, explain the behavioral differences, and attach screenshots or video PoC. Maintain a professional, non‑adversarial tone.
  5. Submit through the platform’s support portal and follow up politely if no response is received within the stated SLA (typically 7 business days).

Linux/Windows command examples for capturing and comparing traffic:

 Linux: Capture HTTP traffic with tcpdump and analyze with ngrep
sudo tcpdump -i any -s 0 -w capture.pcap
ngrep -q -W byline "GET /api/users/" capture.pcap

Windows: Use curl to test endpoint with different user contexts
curl -X GET "https://target.com/api/users/123" -H "Authorization: Bearer <token_userA>"
curl -X GET "https://target.com/api/users/123" -H "Authorization: Bearer <token_userB>"
  1. IDOR and Broken Access Control: The Vulnerability That Refuses to Die

Insecure Direct Object Reference (IDOR) remains one of the most common and impactful web vulnerabilities, frequently ranking in the OWASP Top 10 under Broken Access Control (A01:2021). It occurs when an application exposes internal object identifiers (like user IDs, order numbers, or file paths) in URLs or API parameters and fails to verify that the requesting user is authorized to access that object.

IDOR can manifest as horizontal privilege escalation (accessing another user’s data at the same privilege level) or vertical privilege escalation (accessing administrative functions as a regular user). The core issue is that the application trusts the user‑supplied identifier without enforcing server‑side authorization.

Step‑by‑step guide for IDOR discovery and testing:

  1. Parameter discovery: Identify all user‑controllable parameters that reference objects—numeric IDs (id=123), UUIDs, encoded values, or file names.
  2. Baseline request capture: Log in as User A and capture a legitimate request to access their own resource (e.g., GET /profile?user_id=1001).
  3. Modify the identifier: Change the `user_id` parameter to a value belonging to User B (e.g., user_id=1002) and replay the request using Burp Repeater.
  4. Observe the response: If the server returns User B’s data without an authorization error, you’ve confirmed a horizontal IDOR.
  5. Test vertical escalation: Attempt to access administrative endpoints (e.g., /admin/users) using a low‑privilege session token.

Burp Suite configuration for automated IDOR testing:

  • Install the Autorize or AuthzTester extension to automate role‑based access control tests.
  • Use Intruder with a payload list of user IDs to enumerate accessible resources.
  • Leverage Repeater Strike (AI‑powered) to analyze responses and flag potential IDOR patterns.

API testing with curl and Postman:

 Linux: Test horizontal IDOR with curl
curl -X GET "https://api.target.com/v1/users/1002" -H "Authorization: Bearer $TOKEN_USER_A"

Windows (PowerShell): Similar test
Invoke-RestMethod -Uri "https://api.target.com/v1/users/1002" -Headers @{Authorization="Bearer $TOKEN_USER_A"}
  1. Prevention and Mitigation: Building Access Control That Holds

Preventing IDOR requires a defense‑in‑depth approach that never trusts client‑side input. The most reliable strategy is to treat every request as untrusted and enforce authorization checks on every object access.

Step‑by‑step guide for implementing IDOR‑resistant design:

  1. Eliminate direct object references where possible. Instead of /api/users/:id, use /api/me—the server already knows the authenticated user’s identity from the session.
  2. Use indirect reference maps. Replace direct IDs with temporary, session‑specific tokens that map to the actual object ID on the server side.
  3. Enforce authorization at the data layer. Every database query should include the authenticated user’s ID as a filter, ensuring they can only access their own records.
  4. Use non‑sequential, unpredictable identifiers (e.g., UUID v4) as a defense‑in‑depth measure—but never as a replacement for proper authorization.
  5. Conduct regular security testing with multiple user accounts to identify authorization gaps.

Example: Node.js/Express middleware for object‑level authorization:

// Express middleware to check object ownership
const authorizeOwnership = (model) => async (req, res, next) => {
const objectId = req.params.id;
const userId = req.user.id;

const object = await model.findById(objectId);
if (!object) return res.status(404).json({ error: 'Not found' });

// Critical: Verify ownership before returning data
if (object.userId !== userId) {
return res.status(403).json({ error: 'Forbidden' });
}
req.object = object;
next();
};

// Usage: GET /api/orders/:id
router.get('/orders/:id', authorizeOwnership(Order), (req, res) => {
res.json(req.object);
});
  1. The Art of the Bug Report: Documentation That Wins Appeals

A technically sound finding is worthless if it’s poorly communicated. HMOURI’s success underscores that clear documentation, precise scope definition, and strong evidence can transform a rejected report into a validated one.

Step‑by‑step guide for crafting an appeal‑ready bug report:

  1. Start with a clear, descriptive title that includes the vulnerability type, endpoint, and impact (e.g., “IDOR in `/api/v2/orders` Allows Horizontal Privilege Escalation”).
  2. Provide a concise summary that explains the vulnerability in plain language, then drill down into technical details.
  3. Include reproducible steps with exact requests and responses. Use code blocks for HTTP traffic.
  4. Attach visual evidence—screenshots, screen recordings, or GIFs that demonstrate the exploit.
  5. Quantify the risk using CVSS metrics and explain the business impact (data exposure, financial loss, compliance breach).
  6. Suggest remediation—specific code changes or configuration updates that would fix the issue.
  7. Maintain a professional tone throughout; avoid accusatory language and focus on constructive collaboration.

Example report template snippet:

IDOR in GET /api/users/{id} – Horizontal Privilege Escalation Exposes PII

Summary: The endpoint /api/users/{id} lacks server‑side authorization checks,
allowing any authenticated user to access another user’s full profile data by
modifying the `id` parameter.

Steps to Reproduce:
1. Log in as user A (ID: 1001) and capture the request to GET /api/users/1001.
2. Change the ID to 1002 (user B) and replay the request.
3. Observe that user B’s full profile (name, email, phone, address) is returned.

Impact: Exposure of sensitive PII for all users (CVSS 7.5 – High).

Remediation: Implement server‑side authorization to verify that the
authenticated user owns the requested resource before returning data.

5. Responsible Disclosure: Navigating Ethics and Platform Rules

HMOURI noted that “responsible disclosure is still in progress,” highlighting the importance of ethical handling. Bug bounty hunters must balance the desire for recognition with the obligation to protect users.

Step‑by‑step guide for responsible disclosure:

  1. Never test on production systems without explicit authorization. Use staging environments or authorized bug bounty targets only.
  2. Follow the platform’s rules of engagement regarding scope, testing limits, and data handling.
  3. Report privately through the designated channel—never publicly disclose a vulnerability before it’s fixed.
  4. Allow reasonable time for remediation (typically 30–90 days) before considering public disclosure.
  5. Coordinate with the vendor on patch validation and public announcement timing.

What Undercode Say:

  • A duplicate classification is not a permanent rejection—it can be overturned with precise, evidence‑based technical arguments that highlight behavioral or impact differences.
  • Clear documentation, professional communication, and a thorough understanding of the affected endpoint’s authorization logic are as critical as the initial discovery.
  • IDOR and broken access control remain pervasive because developers often assume that obscuring identifiers (via UUIDs or encoding) is sufficient—but without server‑side authorization checks, these are merely speed bumps, not barriers.
  • The appeal process is not just about getting a bounty; it’s about refining your analytical skills and learning how to articulate complex security issues to non‑technical stakeholders.
  • In the evolving landscape of AI‑assisted testing tools (e.g., Burp AI, Repeater Strike), human judgment and contextual understanding remain irreplaceable—automation finds patterns, but only a researcher can interpret business impact.
  • Effective bug reports are those that make it easy for triage teams to reproduce and validate the issue—saving them time increases the likelihood of your report being prioritized.
  • Responsible disclosure isn’t just an ethical obligation; it builds your reputation as a trusted researcher and opens doors to private programs and higher bounties.
  • The ability to distinguish your finding from prior art—through method, scope, or impact—is a skill that separates top‑tier hunters from the rest.
  • Always document everything: every request, response, and step taken. This not only supports your appeal but also serves as a reusable knowledge base for future research.
  • Ultimately, the bug bounty ecosystem thrives on collaboration—researchers who engage constructively with program owners, rather than adversarial, tend to achieve better outcomes for everyone.

Prediction:

  • +1 The trend toward AI‑powered bug bounty platforms will accelerate, with tools like Burp AI and Repeater Strike automating initial triage and even suggesting appeal arguments based on behavioral analysis.
  • +1 Platforms will increasingly adopt differential reward systems for duplicate reports that provide new technical insights or expanded attack surfaces, encouraging researchers to submit nuanced findings even after a duplicate classification.
  • -1 As automation lowers the barrier to entry, the volume of low‑quality, duplicate submissions will surge, making it harder for high‑signal reports to get timely attention—researchers will need to invest even more in report quality to stand out.
  • -1 The growing reliance on obfuscated identifiers (UUIDs, hashes) may lull developers into a false sense of security, leading to a resurgence of IDOR vulnerabilities where predictable generation algorithms are discovered.
  • +1 The appeal process exemplified by HMOURI will become a formalized feature on major platforms, with clear guidelines and SLAs for reconsideration, reducing researcher frustration and improving ecosystem fairness.
  • +1 Cross‑platform sharing of duplicate fingerprints and vulnerability intelligence will reduce redundant reporting, allowing researchers to focus on novel, high‑impact findings rather than competing for the same low‑hanging fruit.

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