SQL Injection

What is SQL Injection?

SQL Injection is a code injection technique that exploits vulnerabilities in an application's software by allowing attackers to interfere with the queries that an application makes to its database. It is one of the most common and dangerous security threats to web applications.

How SQL Injection Works

When a web application uses unsanitized input from users in SQL queries, an attacker can manipulate the input to execute arbitrary SQL code. For example:

SELECT * FROM Users WHERE username = '$username';

If the $username variable is derived from user input without proper validation or sanitization, an attacker could enter:

' OR '1'='1'; --

The resulting query would be:

SELECT * FROM Users WHERE username = '' OR '1'='1'; --';

This would always return true, potentially giving the attacker unauthorized access to user data.

Types of SQL Injection

• In-band SQL Injection: The most common type, where the attacker uses the same channel to launch the attack and gather results.
• Inferential SQL Injection: The attacker reconstructs the database structure by sending queries and observing the application's response.
• Out-of-band SQL Injection: Data is retrieved using a different channel, such as sending data to a remote server.

Preventing SQL Injection

To protect your application from SQL Injection attacks, follow these best practices:

• Use Prepared Statements: Always use prepared statements with parameterized queries to ensure user input is treated as data, not code.

$stmt = $conn->prepare("SELECT * FROM Users WHERE username = ?");
$stmt->bind_param("s", $username);
$stmt->execute();

• Input Validation: Validate and sanitize all user inputs. Ensure that inputs conform to the expected format.
• Least Privilege Principle: Use the least privilege principle for database accounts. Ensure that the database user account used by your application has the minimum permissions necessary.
• Error Handling: Avoid displaying detailed error messages to users that can reveal information about your database structure.

Example of a Vulnerable Query

$username = $_POST['username']; // User input
$query = "SELECT * FROM Users WHERE username = '$username'";
$result = mysqli_query($conn, $query);

Example of a Secure Query

$stmt = $conn->prepare("SELECT * FROM Users WHERE username = ?");
$stmt->bind_param("s", $username); // User input
$stmt->execute();
$result = $stmt->get_result();

Conclusion

SQL Injection is a serious security risk that can lead to unauthorized access to sensitive data. By following best practices such as using prepared statements and validating user input, you can significantly reduce the risk of SQL Injection vulnerabilities in your applications.