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Introduction:
Bug bounty hunting is more than just scanning for vulnerabilities; it requires a deep understanding of access control mechanisms, authentication flows, and API logic. This article dissects real‑world techniques used by top security researchers to identify and exploit IDOR, privilege escalation, and auth bypass flaws – turning overlooked endpoints into paid bounties.
Learning Objectives:
- Master manual and automated testing for broken access controls in web apps and APIs.
- Learn to craft proof‑of‑concept exploits using Linux, Windows, and proxy tools.
- Understand mitigation strategies and how to write professional bug reports.
You Should Know:
- Identifying IDOR in REST APIs: A Step‑by‑Step Burp Suite Approach
Step‑by‑step guide:
IDOR (Insecure Direct Object References) occurs when an application exposes internal object identifiers (e.g., user ID, order number) without proper authorization checks. Attackers modify these identifiers to access unauthorized data.
How to test for IDOR:
- Intercept requests using Burp Suite (or OWASP ZAP). Log in as user A and navigate to a resource like
/api/profile?user_id=123. - Change the parameter to another valid ID (e.g.,
user_id=124). Forward the request. - Observe the response – if you see another user’s data, you’ve found an IDOR.
- Automate using Burp Intruder with a wordlist of sequential IDs.
Linux command (curl) to test IDOR:
curl -X GET "https://target.com/api/order/1001" -H "Cookie: session=abc123" | jq .
Change 1001 to 1002, 1003...
for id in {1001..1010}; do curl -s "https://target.com/api/order/$id" -H "Cookie: session=abc123" | grep -i "order_id" && echo "Possible IDOR at $id"; done
Windows PowerShell equivalent:
1..1010 | ForEach-Object { $id=$_; Invoke-WebRequest -Uri "https://target.com/api/order/$id" -Headers @{Cookie="session=abc123"} | Select-Object Content }
Mitigation: Use indirect references (e.g., UUIDs), enforce server‑side authorization for every object access, and avoid exposing internal IDs in URLs.
- Privilege Escalation via Horizontal & Vertical Boundary Breaking
Step‑by‑step guide:
Horizontal escalation accesses same‑level user data (e.g., user A → user B). Vertical escalation grants admin privileges to a low‑privileged user.
Testing for horizontal escalation:
- Look for endpoints like `/admin/userlist` or `/api/admin/stats` while logged in as a regular user. If accessible, that’s vertical escalation.
- For horizontal, replace `userId` or `accountId` parameters with another user’s value. Also check batch endpoints like `/api/users?ids=101,102` – try adding an extra ID.
Using ffuf for fuzzing roles:
ffuf -u "https://target.com/api/admin/users" -H "Authorization: Bearer user_token" -w roles.txt -fc 403,401
– `roles.txt` contains common role IDs or headers like X-Forwarded-For: 127.0.0.1, X-Original-URL: /admin.
Burp extension: Use “Autorize” to automatically test for privilege escalation by replaying requests with lower‑privileged sessions.
Mitigation: Implement role‑based access control (RBAC) on the server for every endpoint; never trust client‑side role indicators.
3. Exploiting Mass Assignment in Modern Frameworks
Step‑by‑step guide:
Mass assignment occurs when an API binds user input directly to internal model attributes. Attackers add extra parameters (e.g., isAdmin=true, role=superuser) to create or update records with elevated privileges.
How to test:
- Capture a POST/PUT request to update a profile, e.g.,
{"name":"test","email":"[email protected]"}.
2. Add an unexpected parameter: `{“name”:”test”,”email”:”[email protected]”,”isAdmin”:true,”role”:”admin”}`.
- If the application sets `isAdmin=true` in the backend, you’ve successfully mass‑assigned an admin role.
Payload examples (add to JSON or form data):
isAdmin=1 role=administrator privilege_level=99 can_delete=true
Tool automation with Arjun (parameter discovery):
arjun -u https://target.com/api/user/update -d '{"name":"test"}' -m POST --json
Mitigation: Use allowlists for writable fields (e.g., `$fillable` in Laravel, `@Column(updatable=false)` in Java), and never bind user input directly to models.
- JSON Web Token (JWT) Algorithm Confusion & Signature Bypass
Step‑by‑step guide:
Developers sometimes misconfigure JWT verification, allowing attackers to change the algorithm to `none` or to symmetric HS256 (when public key is known).
Testing steps:
- Capture a JWT from a request. Decode it using `jwt.io` or CLI.
- Change the `alg` header from `RS256` to
HS256. - Sign the modified token with the public key (obtainable from `/jwks.json` or
.well-known/jwks). - Replay the request. If accepted, the server used the public key as a symmetric secret – a critical flaw.
Linux commands using `jwt_tool` and `python-jose`:
Install jwt_tool
git clone https://github.com/ticarpi/jwt_tool
python3 jwt_tool.py <JWT> -T -S hs256 -p public_key.pem
Python one‑liner to forge HS256 with known public key
python3 -c "import jwt; print(jwt.encode({'user':'admin'}, open('public.pem').read(), algorithm='HS256'))"
Mitigation: Enforce algorithm whitelisting (only RS256/ES256), validate `alg` against a strict list, never trust alg: none.
- Cloud Hardening for Bug Bounty Hunters: Misconfigured S3 Buckets & Lambda Over‑Privilege
Step‑by‑step guide:
Cloud assets often leak data via overly permissive IAM roles or public storage.
Testing S3 bucket misconfigurations:
- Look for bucket names in JS files, source code, or via subdomain enumeration (e.g., `assets.target.com` →
target-assets.s3.amazonaws.com).
2. Test listing permissions:
aws s3 ls s3://target-assets --no-sign-request aws s3 cp s3://target-assets/secret.txt . --no-sign-request
3. Check bucket ACLs:
aws s3api get-bucket-acl --bucket target-assets --no-sign-request
Testing Lambda over‑privilege (if you have AWS access):
- Assume a low‑privilege role and attempt to invoke a production lambda:
aws lambda invoke --function-name adminFunction output.txt
- If successful, the role’s IAM policy is too permissive.
Mitigation: Block public ACLs, enforce bucket policies with explicit denies, and use least‑privilege IAM roles with resource‑based conditions.
- Windows Active Directory Privilege Escalation for Hybrid Bug Bounties
Step‑by‑step guide:
Many bug bounty programs include internal AD environments where misconfigured Kerberos or ACLs lead to domain compromise.
Common AD misconfigurations to test (if authorized):
- Kerberoasting: Extract service tickets for accounts with SPNs (Service Principal Names). Crack offline.
PowerShell on Windows Add-Type -AssemblyName System.IdentityModel Use Rubeus or Invoke-Kerberoast .\Rubeus.exe kerberoast /outfile:hashes.txt
- AS-REP Roasting: Find users without pre‑authentication.
.\Rubeus.exe asreproast /format:hashcat /outfile:asrep.txt
- BloodHound collection to map attack paths:
Linux with SharpHound ./SharpHunt -c All -d target.local
Mitigation: Enforce strong service account passwords, enable Kerberos pre‑authentication for all users, and regularly audit ACLs using tools like PingCastle.
7. Writing Professional Bug Reports That Get Paid
Step‑by‑step guide:
A high‑quality report increases bounty value and triage speed.
Structure:
- Concise and technical – “IDOR in /api/v2/orders allows viewing any user’s order history.”
2. Description: Steps to reproduce (with exact requests/responses).
- Impact: Real‑world damage (e.g., “Attacker can view all orders including PII and payment info”).
- Proof of Concept (PoC): Provide a curl command or Burp replay file.
- Mitigation suggestion: Use UUIDs and server‑side auth check.
6. Affected versions/environment.
Example PoC curl:
curl -X GET "https://target.com/api/orders/12345" -H "Authorization: Bearer victim_token" --cookie "session=attacker_cookie"
Tools to automate reporting: Use `grep` and `jq` to extract evidence, or Burp’s “Save item” as JSON.
What Undercode Say:
- Key Takeaway 1: Broken access control remains the 1 most critical web vulnerability (OWASP Top 10). Every parameter and endpoint is a potential privilege escalation vector.
- Key Takeaway 2: Successful bug hunting requires a hybrid toolkit – combining automated fuzzing (ffuf, Arjun) with manual logic analysis (JWT alg confusion, mass assignment).
- Analysis: The LinkedIn conversations hint at a vibrant, competitive bounty community where sharing program names is guarded. To succeed, researchers must go beyond scanners, mastering how developers think – and mis‑implement – authorization. Cloud and AD misconfigurations are the new goldmines, as traditional XSS/SQLi get saturated. Expect stricter API schemas (GraphQL, gRPC) to shift the battle toward business logic flaws.
Prediction:
By 2027, AI‑powered fuzzing frameworks will automate 70% of basic IDOR and privilege escalation checks, forcing bug hunters to specialize in complex state‑machine bypasses (e.g., race conditions in async APIs, cross‑tenant SSO misconfigurations). Platforms will introduce real‑time dynamic authorization testing, making static parameter tampering obsolete. The bounty $ time will belong to those who master cloud privilege escalation and zero‑day logic flaws in machine‑learning pipelines.
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IT/Security Reporter URL:
Reported By: Jignesh Vaniya – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
