How to Prevent SQL Injection in PHP: Complete Guide

SQL injection is one of the most common security vulnerabilities in web applications. It occurs when an attacker manipulates a SQL query by injecting malicious input, potentially gaining unauthorized access to your database. This guide will teach you how to prevent SQL injection in PHP and secure your application.

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What is SQL Injection?

SQL injection is a code injection technique where attackers exploit vulnerabilities in your database queries. For example:

phpCopy code// Vulnerable SQL query
$username = $_GET['username'];
$password = $_GET['password'];
$query = "SELECT * FROM users WHERE username = '$username' AND password = '$password'";

If malicious input like "' OR '1'='1" is passed, it can bypass authentication.

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How to Prevent SQL Injection in PHP?

1. Use Prepared Statements with Parameterized Queries
   Prepared statements separate SQL code from user input, ensuring malicious input is not executed as code.

phpCopy code// Secure example using PDO
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = :username AND password = :password");
$stmt->bindParam(':username', $username, PDO::PARAM_STR);
$stmt->bindParam(':password', $password, PDO::PARAM_STR);
$stmt->execute();

2. Validate and Sanitize User Input
   Ensure all user input meets expected criteria using functions like filter_input() or custom validation logic.

phpCopy code$username = filter_input(INPUT_GET, 'username', FILTER_SANITIZE_STRING);

3. Escape Strings for Legacy Code
   If you cannot use prepared statements, escape special characters with mysqli_real_escape_string().

phpCopy code$username = mysqli_real_escape_string($conn, $_GET['username']);

4. Use Stored Procedures
   Stored procedures execute precompiled SQL, minimizing the risk of injection.
5. Implement Least Privilege for Database Users
   Assign minimal permissions to the database user your application uses.
6. Regularly Update Your PHP and Database Software
   Stay up-to-date with the latest security patches for PHP and your database management system.

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Why SQL Injection Prevention is Important?

Preventing SQL injection is critical to safeguarding sensitive data like user credentials, financial information, and proprietary business data. Failing to secure your application can result in:

• Data breaches
• Legal consequences
• Damage to your reputation

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Key Takeaways

• Always use prepared statements and parameterized queries in PHP.
• Validate and sanitize all user inputs.
• Keep your PHP and database software up-to-date.

By following these best practices, you can effectively prevent SQL injection and secure your application.

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FAQ: SQL Injection Prevention in PHP

Q: Can input validation alone prevent SQL injection?
A: While input validation reduces risk, combining it with prepared statements ensures robust protection.

Q: Is PDO better than MySQLi for SQL injection prevention?
A: Both PDO and MySQLi offer prepared statements, but PDO is more versatile for different databases.