These attacks can be devastating, potentially allowing an attacker to view, modify, or delete data. Here are some strategies to prevent SQL injection attacks:

Use prepared statements (Parameterized queries)

Instead of creating SQL queries with string concatenation, use prepared statements. These involve setting up the SQL code with placeholders for data, and then passing in the data as parameters. This way, the data is separated from the SQL code and can't be used to modify it. In PHP, this can be done with the PDO extension or with mysqli. In Java, it can be done with PreparedStatement objects.

Here's an example of a prepared statement using PHP's PDO extension:

$stmt = $pdo->prepare("SELECT * FROM users WHERE email = :email");
$stmt->execute(['email' => $email]);
$user = $stmt->fetch();

Use stored procedures

These are SQL statements that are stored in the database and can be called from the application. Since they're defined in the database, they can't be modified by user input. However, they can still be vulnerable if they're improperly written, such as by including unparameterized dynamic SQL.

Here's an example of a stored procedure in MySQL

DELIMITER //
CREATE PROCEDURE GetUserByEmail(IN userEmail VARCHAR(255))
BEGIN
SELECT * FROM users WHERE email = userEmail;
END //
DELIMITER ;

Escaping user input

This involves processing nput to ensure that any characters that have special meaning in SQL (like single quotes) are escaped, which means that they're treated as literal characters and not as part of the SQL syntax. This is more prone to errors than using prepared statements or stored procedures, so it's generally used as a last resort when the others aren't possible.

$email = $pdo->quote($email);
$query = "SELECT * FROM users WHERE email = $email";
$user = $pdo->query($query)->fetch();

Least privilege principle

Limit the permissions of the database account used by the application to only what it needs. This way, even if an attacker can perform SQL injection, they won't be able to perform actions like deleting tables.This involves creating a database user with only the necessary permissions. Here's an example in MySQL

CREATE USER 'appuser'@'localhost' IDENTIFIED BY 'password';
GRANT SELECT ON database.users TO 'appuser'@'localhost';

Input validation

While this can't completely stop SQL injection by itself, it's still useful as part of a defense in depth strategy. This involves checking user input to make sure it's in a valid format before using it.

You can use PHP's filter functions to validate input. For example, to validate an email address, you can do:

if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
echo("Invalid email format");
}

Use web application firewalls

These can help filter out malicious data and can block known attack patterns. However, they can't catch every possible SQL injection, so they should be used alongside the other strategies, not instead of them.

Regularly update and patch your systems

SQL Injection is a well-known type of attack, and as such, many database management systems and web programming languages regularly update their software to deal with known vulnerabilities. Always keep your systems up-to-date.

Error handling

Proper error handling in your application can prevent attackers from obtaining valuable information about your database structure. Displaying database error messages to the user can provide an attacker with clues on how to fine-tune their attack. Instead, log errors internally and display a generic error message to the user.

Suppress database error messages in your production environment. For example

ini_set('display_errors', '0'); // Don't display errors to users

Log errors for your internal review

error_log($e->getMessage()); // Assuming $e is an exception object

White-List input validation

This is an approach where only specified and accepted inputs are allowed, as opposed to black-listing bad or malicious inputs. This approach is safer as it's impossible to list all potential malicious inputs, but you can list all acceptable inputs.

For example, if you only accept certain values for a user's role, check the input against the acceptable values:

$valid_roles = ['user', 'admin', 'moderator'];
if (!in_array($role, $valid_roles)) {
echo("Invalid role");
}

Database account management

Do not use the "root" or "admin" database account for application connections. Instead, create specific accounts for each application with the lowest level of privileges necessary.

Like the Least Privilege Principle, create specific accounts for each application

CREATE USER 'appuser'@'localhost' IDENTIFIED BY 'password';
GRANT SELECT, INSERT, UPDATE ON database.users TO 'appuser'@'localhost';

Database configuration

Configure your database to reduce the potential damage of an SQL injection attack. This includes steps such as disabling the xp_cmdshell stored procedure in MS SQL Server, which can be used to issue OS commands, and limiting the commands a database user can execute.Disable potentially dangerous features in your database. For example, in MySQL, you can disable multiple statements for a particular connection

$pdo = new PDO("mysql:host=localhost;dbname=database", 'username', 'password', [
PDO::ATTR_EMULATE_PREPARES => false
]);

Use an ORM (Object Relational Mapping) library

Many popular programming languages have ORM libraries which help in dealing with database interactions and which have features to prevent SQL injection.

Here's an example of fetching a user with the Doctrine ORM:

$userRepository = $entityManager->getRepository('User');
$user = $userRepository->findOneByEmail($email);

Regularly conduct security audits and vulnerability assessments

Regular audits help identify any potential weaknesses or loopholes that might be exploited by attackers.

Educate and train your development team

Your security is only as strong as the knowledge of your team. Make sure all developers are aware of the risks of SQL injection attacks and how to prevent them.

SQL injection testing

Use automatic tools and manual testing to search for possible SQL Injection vulnerabilities.

Remember, security is about layers. While no single strategy can fully protect against SQL injection, using several of them together can greatly reduce the risk