An attacker can interfere with the database queries made by an application through SQL Injection (SQLi) a web security vulnerability. By manipulating input fields, attackers can execute arbitrary SQL code, potentially compromising the database and gaining unauthorized access to sensitive data.
How It Works:
When a web application constructs SQL queries using user input without proper validation or sanitization, an attacker can inject malicious SQL code. This can allow the attacker to manipulate the database in various ways, such as reading data, modifying records, or even executing administrative operations.
Example Scenario:
Consider a simple SQL query that retrieves user information based on a username provided by a user:
If the application directly uses user input without sanitization, an attacker could provide input like:
The resulting SQL query would become:
By using this query, all users in the database can be returned, bypassing authentication or authorization checks.
Bad Code Example (PHP):
$query = "SELECT * FROM users WHERE username = '$username' AND password = '$password'";
$result = mysqli_query($conn, $query); // Vulnerable to SQL Injection
Potential Risks
- Data Theft: Attackers can extract sensitive data from the database, including personal information, passwords, and credit card numbers.
- Data Manipulation: Attackers can modify or delete records in the database, leading to data loss or corruption.
- Administrative Access: In some cases, attackers can gain administrative privileges and perform actions such as creating new users or altering database structures.
- Denial of Service (DoS): SQL injection can be used to crash the database server or make it unavailable.
Prevention Strategies
- Prepared Statements and Parameterized Queries: Preparated statements can be used with parameterized queries to ensure that user input is treated as data, not executable code.
- Input Validation: Validate and sanitize all user inputs to ensure they conform to expected formats.
- Stored Procedures: Use stored procedures to encapsulate SQL queries and limit direct user input in queries.
- Database Permissions: Restrict database user permissions to limit what actions can be performed, reducing the impact of a successful SQL injection.
- Web Application Firewalls (WAF): Implement WAFs to detect and block potential SQL injection attempts.
- Error Handling: Implement proper error handling to avoid exposing database errors to users, which could provide clues for exploitation.
Good Code Example (using PHP and PDO):
$stmt = $pdo->prepare('SELECT * FROM users WHERE username = :username AND password = :password');
$stmt->execute(['username' => $username, 'password' => $password]);