How to prevent SQL injection attacks using PHP forms

SQL injection attack is a relatively common method of network attack at present. It refers to constructing illegal SQL statements to achieve illegal operations on the database, thereby obtaining sensitive information, destroying data, etc. In PHP applications, forms are used as a means of inputting data on the front end, and the data entered in the form is likely to be used as a component of a SQL query statement. Therefore, preventing SQL injection attacks is crucial to the security of the application. This article will introduce how to use PHP forms to prevent SQL injection attacks.

1. What is a SQL injection attack?

SQL injection attack refers to an attacker entering malicious SQL code into a web form or input box to trick the database system into executing malicious instructions. Purpose. Therefore, attackers can view, modify, and delete data through SQL injection attacks, or perform more malicious behaviors through some advanced techniques.

SQL injection attacks are currently widespread in many applications. This is because many developers don't take enough into account the security issues caused by lack of input validation. Once an attacker discovers such a vulnerability, they can easily exploit it to gain access to sensitive information, thereby obtaining critical data or tampering with the application's database.

2. How to use PHP forms to prevent SQL injection attacks

1. Dynamic filtering of user input

Avoid using mindless string splicing methods, but instead Dynamically process user-entered data. Usually we can use functions such as "mysqli_real_escape_string()" for escaping so that the input data will not be executed as a SQL statement in the database. This function has good escaping capabilities and can handle all characters, but in practice it may cause some performance loss.

Sample code:

$con = mysqli_connect("localhost", "my_user", "my_password", "my_db");
if (! $con) {

}

$username = mysqli_real_escape_string($con, $_POST['username']);
$password = mysqli_real_escape_string($con, $_POST[' password']);
$sql = "SELECT * FROM users WHERE username='$username' and password='$password'";
$result = mysqli_query($con, $sql);
?>

2. Use PDO prepared statements

PDO prepared statements provide a safer way to prevent SQL injection attacks. Using prepared statements can prevent attackers from constructing malicious SQL statements due to SQL injection attacks, ensuring the security of the application.

Principle of prepared statements: Use placeholders to replace actual variables, and then pass in parameters during the execution phase. Because this existing placeholder has been specially processed, the problem of SQL injection can be avoided. PDO provides the PDOStatement class, through the interface of this class, SQL preprocessing can be completed. Here is an example:

$stmt = $dbh->prepare("SELECT * FROM users WHERE username=:username and password=:password");
$ stmt->bindParam(':username', $username);
$stmt->bindParam(':password', $password);
$stmt->execute();
? >

3. Prohibit the execution of multiple statements

Never execute multiple SQL statements easily. Executing multiple SQL statements increases the risk of SQL injection attacks on the program. Therefore, do not execute multiple SQL statements together.

Execute only one item at a time and check the execution results. The following is an example of filtering multiple statements:

if (substr_count($_GET['id'], ' ') > 0) {
die('Error' );
}
?>

4. Prohibit the use of special characters

For dangerous special characters, such as single quotes, commas, brackets, etc., you can Filter using the filter functions provided in PHP.

Sample code:

$username = filter_var($_POST['username'], FILTER_SANITIZE_STRING);
$password = filter_var($_POST[' password'], FILTER_SANITIZE_STRING);
?>

Summary:

In today’s Internet era, SQL injection attacks have become a security issue that must be paid attention to in the field of network security. Therefore, for PHP applications, especially those involving databases, it is crucial to clearly understand and use the methods described above to ensure the security of the application. When developing PHP applications, we should always keep the risk of SQL injection attacks in mind and use PHP forms correctly to prevent them, thereby protecting the security of the application.

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