SQL Injection Attack Principles and Prevention

SQL Injection Attack Principles and Prevention

Problem Description
SQL injection is a common web security vulnerability where attackers insert malicious SQL code into input fields of an application, tricking the database server into executing unauthorized SQL commands, thereby stealing, tampering with, or deleting data.

Solution Process

Understand the Basic Principles of SQL Injection
- Normal scenario: When a user logs in by entering a username and password, the application generates an SQL query:
```
SELECT * FROM users WHERE username = 'input_username' AND password = 'input_password'
```
- Attack scenario: The attacker inputs admin' -- in the username field and any value for the password.
  - The generated statement becomes:
```
SELECT * FROM users WHERE username = 'admin' --' AND password = 'any_password'
```
  - -- denotes a comment in SQL, causing the subsequent condition to be ignored, potentially allowing the attacker to log in as admin.
Analyze SQL Injection Attack Methods
- Union Query Injection: Using the UNION operator to retrieve data from other tables.
```
' UNION SELECT credit_card FROM payments --
```
- Boolean Blind Injection: Determining data content based on true/false responses from the page.
```
' AND substring(database(),1,1) = 'a' --
```
- Time-Based Blind Injection: Using delay functions to determine the truth of conditions.
```
' AND IF(1=1,sleep(5),0) --
```
Master Key Techniques for Preventing SQL Injection
- Use Parameterized Queries (Prepared Statements)
```
# Wrong approach (string concatenation)
cursor.execute("SELECT * FROM users WHERE username = '" + username + "'")

# Correct approach (parameterized query)
cursor.execute("SELECT * FROM users WHERE username = %s", (username,))
```
- Implement the Principle of Least Privilege: Grant database users only necessary permissions.
- Input Validation and Filtering: Escape special characters.
- Use Web Application Firewalls (WAF) to detect malicious requests.
Practical Defense Measures
- Encapsulate database error messages to avoid leaking sensitive information.
- Conduct regular security audits and vulnerability scans.
- Provide secure coding training for development teams.
- Use ORM frameworks (e.g., Hibernate, MyBatis) to reduce handwritten SQL.

By understanding attack principles and implementing multi-layered defenses, SQL injection attacks can be effectively prevented, ensuring data security.