PHP implements secure programming: SQL injection and defense

Secure Programming with PHP: SQL Injection and Defense

Nowadays, the Internet is booming, and websites and applications are becoming more and more popular. With this comes growing security threats. One of the most common attack methods is SQL injection. SQL injection attacks use input data to modify or tamper with SQL commands, and then access, modify, and delete the contents of the back-end database. This article will introduce the principles and defensive measures of SQL injection attacks, and how to implement secure programming in PHP.

The principle of SQL injection attack:

The principle of SQL injection attack is very simple: the attacker overwrites the original data with malicious malicious data, thereby interfering with and destroying the data processing process. Since SQL queries are usually constructed by a program based on data entered by the user, an attacker can add special characters to the input to modify the query to the results the attacker wants.

The following is a simple sample code:

$user = $_POST['user'];
$password = $_POST['password'];

//查询用户是否存在
$sql = "SELECT * FROM users WHERE username='$user' AND password='$password'";
$result = mysqli_query($conn, $sql);

If an attacker enters the following code:

' OR '1'='1

, the constructed SQL query statement will become:

SELECT * FROM users WHERE username='' OR '1'='1' AND password=''

This will cause the query statement to always return a true value, allowing the attacker to bypass authentication and access, modify or delete the contents of the database.

Defense measures:

There are many ways to defend against SQL injection attacks. The following are some commonly used measures:

1. Use prepared statements:

Prepared statements are an effective way to prevent SQL injection attacks. They use placeholders to replace variables in the query statement. These placeholders are automatically escaped by the program and the data is checked.

The following is a sample code using prepared statements:

$user = $_POST['user'];
$password = $_POST['password'];

//使用预处理语句查询用户是否存在
$stmt = $conn->prepare("SELECT * FROM users WHERE username=? AND password=?");
$stmt->bind_param("ss", $user, $password);
$stmt->execute();
$result = $stmt->get_result();

2. Filtering user input:

Before reading and manipulating user input data, It must be filtered and verified. You can use PHP's built-in functions to filter user input, such as htmlspecialchars() or mysqli_real_escape_string().

The following is a sample code that uses the mysqli_real_escape_string() function to filter user input:

$user = mysqli_real_escape_string($conn, $_POST['user']);
$password = mysqli_real_escape_string($conn, $_POST['password']);

//查询用户是否存在
$sql = "SELECT * FROM users WHERE username='$user' AND password='$password'";
$result = mysqli_query($conn, $sql);

3. Minimize user input:

Reduce what the user needs to enter Data can reduce the risk of SQL injection attacks. You can use the form's default values, drop-down menus, radio buttons, etc. to reduce user input, and you can also limit the user's input length.

In actual applications, it is recommended not to use database-related functions to filter or validate user input data. Because these functions may fail due to database locks or other issues, leading to security vulnerabilities.

Conclusion:

SQL injection attack is a common network attack method that can cause serious consequences in a short period of time. However, SQL injection attacks can be effectively defended by using prepared statements, filtering user input, and minimizing user input. Stay safe online by staying vigilant and constantly updating your knowledge.

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