SQL Injection is one of the most common and dangerous security vulnerabilities for websites. This attack method allows malicious users to gain unauthorized access to the database. It can be used to modify data, steal user information, or execute harmful operations on the server.
In this article, I will explain how SQL Injection attacks work and how you can protect against them.
1. How Does SQL Injection Work?
SQL Injection attacks typically exploit security flaws in user input forms, search boxes, or URL parameters.
For example, the following flawed SQL query is vulnerable to attack:
$user = $_GET['user'];
$query = "SELECT * FROM users WHERE username = '$user'";
$result = mysqli_query($conn, $query);
If an attacker inputs the following:
' OR '1'='1
The resulting SQL query becomes:
SELECT * FROM users WHERE username = '' OR '1'='1'
Since the condition '1'='1' is always true, the attacker gains access to all user information!
2. What Can Be Done with SQL Injection?
A SQL Injection attack can be used for several harmful actions:
- Stealing user information: Gaining access to all usernames and passwords.
- Unauthorized access: Logging into administrator accounts.
- Modifying the database: Altering or deleting existing records.
- Server control: In some cases, executing system commands on the server.
3. How to Prevent SQL Injection
The most effective way to prevent SQL Injection attacks is to use prepared statements and parameterized queries.
Use Prepared Statements
Prepared statements separate SQL queries from user input, enhancing security.
Secure Query Using PHP PDO:
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = ?");
$stmt->execute([$user]);
$result = $stmt->fetch();
Secure Query Using MySQLi:
$stmt = $conn->prepare("SELECT * FROM users WHERE username = ?");
$stmt->bind_param("s", $user);
$stmt->execute();
Advantages:
- Prevents SQL Injection attacks.
- Properly processes data.
- Improves performance.
Sanitize User Input
Always validate and filter user input to prevent malicious data.
Example of Secure Input Validation:
$username = filter_input(INPUT_GET, 'user', FILTER_SANITIZE_STRING);
Incorrect Usage (Vulnerable to SQL Injection):
$query = "SELECT * FROM users WHERE username = '" . $_GET['user'] . "'";
This method is not secure!
Use a Web Application Firewall (WAF)
Web security firewalls (WAF) can automatically block malicious SQL queries. Recommended WAF solutions:
- Cloudflare WAF
- ModSecurity
- Sucuri Firewall
Limit Database Privileges
To reduce the impact of SQL Injection attacks, grant minimum necessary database privileges.
Recommended Permissions:
- Restrict SELECT privileges when possible.
- Avoid using the root database account.
- Create separate users for different tasks.
Example: Creating a Read-Only User:
GRANT SELECT ON database_name.* TO 'readonly_user'@'localhost' IDENTIFIED BY 'strongpassword';
Conclusion
SQL Injection attacks can be easily prevented with the right precautions. To secure your database:
- Use prepared statements.
- Always sanitize user input.
- Enable firewalls and permission systems.
By implementing these measures, you can develop a secure web application and protect your data!