What are the best ways to prevent SQL injections in web design?

1 Use parameterized queries

One of the most effective ways to prevent SQL injections is to use parameterized queries, also known as prepared statements. These are SQL queries that separate the structure and the data, and use placeholders for user input. This way, the user input is treated as a literal value, and not as part of the SQL command. Parameterized queries are supported by most programming languages and frameworks, such as PHP, Python, Java, and .NET. For example, in PHP, you can use the PDO library to create and execute parameterized queries, like this:

// Create a parameterized query
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username");
// Bind the user input to the placeholder
$stmt->bindParam(':username', $_POST['username']);
// Execute the query
$stmt->execute();        

2 Validate and sanitize user input

Another way to prevent SQL injections is to validate and sanitize user input before sending it to the database. Validation means checking that the user input meets certain criteria, such as length, format, type, and range. Sanitization means removing or escaping any characters that could interfere with the SQL syntax, such as quotes, semicolons, and comments. You can use built-in functions or libraries to perform validation and sanitization, depending on your programming language and framework. For example, in PHP, you can use the filter_var function to validate user input, and the mysqli_real_escape_string function to sanitize user input, like this:

// Validate user input
if (filter_var($_POST['email'], FILTER_VALIDATE_EMAIL)) {
  // Sanitize user input
  $email = mysqli_real_escape_string($conn, $_POST['email']);
  // Proceed with the query
} else {
  // Reject user input
}        

3 Use stored procedures

A stored procedure is a pre-defined SQL query that is stored in the database and can be called by the application. Stored procedures can help prevent SQL injections by limiting the access and privileges of the user input, and by enforcing a consistent structure and logic for the queries. Stored procedures can also improve the performance and maintainability of your web application, by reducing the network traffic and simplifying the code. To use stored procedures, you need to create them in your database management system, such as MySQL, Oracle, or SQL Server, and then invoke them from your programming language or framework. For example, in MySQL, you can create a stored procedure like this:

-- Create a stored procedure
DELIMITER //
CREATE PROCEDURE get_user (IN user_name VARCHAR(255))
BEGIN
  SELECT * FROM users WHERE username = user_name;
END //
DELIMITER ;        

And then call it from PHP like this:

// Call the stored procedure
$stmt = $pdo->prepare("CALL get_user(:username)");
$stmt->bindParam(':username', $_POST['username']);
$stmt->execute();        

4 Use least privilege principle

The least privilege principle means that you should grant the minimum level of access and permissions to your database and web application, and only for the necessary duration and scope. This way, you can reduce the risk and impact of SQL injections, by limiting what the attacker can do and see. For example, you should use a separate user account for your web application, and only grant it the privileges that it needs to perform its functions, such as SELECT, INSERT, UPDATE, and DELETE. You should also avoid using the root or admin account for your web application, and revoke any unnecessary privileges from other user accounts. You can use the GRANT and REVOKE statements in SQL to manage the privileges of your user accounts, like this:

-- Grant SELECT privilege to web_user on users table
GRANT SELECT ON users TO web_user;
-- Revoke DELETE privilege from web_user on users table
REVOKE DELETE ON users FROM web_user;        

5 Use error handling and logging

Error handling and logging are essential for debugging and monitoring your web application, and for detecting and preventing SQL injections. Error handling means that you should handle any exceptions or errors that occur in your web application, and display appropriate messages to the user and the developer. You should avoid showing the raw SQL errors or stack traces to the user, as they can reveal sensitive information about your database and web application, and help the attacker to refine their SQL injection. You should also use logging to record any events or activities that occur in your web application, such as user input, queries, errors, and responses. You should store the logs in a secure location, and review them regularly to identify any anomalies or suspicious patterns. You can use various tools and frameworks to implement error handling and logging in your web application, such as PHP's error_reporting and error_log functions, or Python's logging module. For example, in PHP, you can use the try-catch block to handle errors, and the error_log function to log errors, like this:

// Try to execute a query
try {
  $stmt = $pdo->query("SELECT * FROM users");
} catch (PDOException $e) {
  // Catch and log the error
  error_log($e->getMessage());
  // Display a generic message to the user
  echo "Something went wrong. Please try again later.";
}        

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?