How to prevent SQL injection attacks using PHP

In the field of network security, SQL injection attacks are a common attack method. It exploits malicious code submitted by malicious users to alter the behavior of an application to perform unsafe operations. Common SQL injection attacks include query operations, insert operations, and delete operations. Among them, query operations are the most commonly attacked, and a common method to prevent SQL injection attacks is to use PHP.

PHP is a commonly used server-side scripting language that is widely used in web applications. PHP can interact with relational databases such as MySQL, but it is also vulnerable to SQL injection attacks. To prevent SQL injection attacks, you first need to understand the principles of SQL injection attacks.

The principle of SQL injection attack is to make unexpected and malicious behavior by modifying part or all of the contents of the SQL query statement. SQL injection attacks are mainly divided into two types: "error injection" and "blind injection". In "error injection", the attacker causes the server to return an error by submitting malicious data. In "blind injection", the attacker will submit malicious data to determine whether the server's response meets expectations, thereby gradually obtaining the required data.

Next, we introduce how to use PHP to prevent SQL injection attacks.

Step 1: Filter user input

Filtering user input is the simplest and most basic method to prevent SQL injection attacks. Filtering input determines how trustworthy it is. Filtering user input can be achieved using functions in PHP.

htmlspecialchars() function is a function in PHP used to filter web form input. This function can convert the html special characters entered by the user (such as <>&) into html entities (such as <>&)

filter_var() function is a function in PHP used to filter user input . This function can verify whether the user input is an integer, whether it is an email, etc. In addition, PHP also provides other filter functions, such as filter_has_var() and filter_input().

Step 2: Use PDO instead of MySQL

PDO is a data access layer in PHP. It is used to access many different types of databases and provides some mechanisms to prevent SQL injection attacks. Unlike MySQLi, PDO is implemented based on an object-oriented approach. The PDO interface can explicitly use parameterized queries to prevent SQL injection attacks. One benefit of using PDO is that its SQL statements can be parameterized by giving placeholders.

The following code example implements PDO to prevent SQL injection attacks:

//连接数据库
$dsn= 'mysql:host=hostname;dbname=databasename;charset=utf8';
$options = array(
   PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,//设置错误模式
   PDO::ATTR_EMULATE_PREPARES => false,//把预处理默认为真
);
try {
   $pdo = new PDO($dsn, $username, $password, $options);
} catch (PDOException $e) {
   print "Error!: " . $e->getMessage() . "<br/>";
   die();
}
//使用PDO进行参数化查询
$stmt = $pdo->prepare('SELECT * FROM user WHERE username = ?');
$stmt->execute(array($_GET['username']));

Step 3: Use mysql_real_escape_string()

The mysql_real_escape_string() function is one of the PHP functions provided by MySQL . It prevents SQL injection attacks by escaping special characters. The mysql_real_escape_string() function will traverse the string and escape special characters such as ', ",,, and
to their safe equivalent forms. When using the mysql_real_escape_string() function, you need to establish a connection with the server and log in first.

Finally, it should be noted that SQL injection attacks are a very common method of network attacks. To prevent SQL injection attacks, you need to always be vigilant and take effective measures, such as filtering user input and using PDO instead MySQL and use the mysql_real_escape_string() function.

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