How to avoid SQL keyword injection attacks in PHP language development?

With the development of the Internet, SQL injection attacks have become a serious problem in network security. SQL injection attack refers to an attack method in which attackers use web application vulnerabilities to submit malicious SQL statements to the server to achieve illegal access and steal sensitive data. As one of the most widely used programming languages ​​in web development, PHP language also faces the risk of SQL injection attacks. In this article, we will introduce how to avoid SQL keyword injection attacks in PHP language development.

1. Understand SQL injection attacks

Before preventing SQL injection attacks, we first need to understand the basic concepts and principles of SQL injection attacks. SQL injection attacks mainly use web applications to incorrectly filter user input data, and pass user input directly to the backend database as part of the SQL statement, allowing attackers to attack and control the database through malicious SQL statements. For example, the following code snippet may be at risk of SQL injection attacks:

<?php
//连接数据库
$con=mysqli_connect("localhost","username","password","my_db");

//获取用户提交的用户名和密码
$username=$_POST['username'];
$password=$_POST['password'];

//构造SQL语句
$sql="SELECT * FROM users WHERE username='".$username."' AND password='".$password."'";

//执行SQL语句
$result=mysqli_query($con,$sql);

// 输出查询结果
while($row=mysqli_fetch_array($result,MYSQLI_ASSOC)){
    echo $row['username']. " " . $row['password'];
}

//关闭数据库连接
mysqli_close($con);
?>

In the above code, the data submitted by the user can be directly passed into the SQL database as part of the SQL statement, and the attacker can use Some means pass malicious SQL statements into the database to attack and control the database. For example, when the password submitted by the user is "123' OR 1=1--", the database will execute the following SQL statement:

SELECT * FROM users WHERE username='user' AND password='123' OR 1=1--'

This SQL statement will query the information of all users in the database, because " 1=1" is always true.

2. Methods to avoid SQL injection attacks

In order to avoid SQL injection attacks, we need to take some measures to protect Web applications from attacks. Here are some common methods:

1. Use parameterized queries

Parameterized queries are an effective way to avoid SQL injection attacks. This method uses predefined SQL statements and parameters, and passes parameter values ​​as input to the database for execution. This method can prevent user-entered data from being directly spliced ​​into SQL statements, thereby protecting web applications from SQL injection attacks. For example, the following code uses a parameterized query:

<?php
//连接数据库
$con=mysqli_connect("localhost","username","password","my_db");

//获取用户提交的用户名和密码
$username=$_POST['username'];
$password=$_POST['password'];

//构造SQL语句
$sql="SELECT * FROM users WHERE username=? AND password=?";

//创建预处理语句
$stmt=mysqli_prepare($con,$sql);

//绑定参数值
mysqli_stmt_bind_param($stmt,"ss",$username,$password);

//执行SQL语句
mysqli_stmt_execute($stmt);

// 迭代查询结果
$result=mysqli_stmt_get_result($stmt);
while($row=mysqli_fetch_array($result,MYSQLI_ASSOC)){
    echo $row['username']. " " . $row['password'];
}

//关闭数据库连接
mysqli_close($con);
?>

2. Filtering input data

Before processing user input data, we can filter it, thus ensuring its security sex. For example, we can use PHP's built-in functions strip_tags(), addslashes(), etc. to filter user input data. These functions can filter out HTML tags, escape special characters, etc. in user input, thereby reducing the risk of SQL injection attacks. For example:

<?php
//连接数据库
$con=mysqli_connect("localhost","username","password","my_db");

//获取用户提交的用户名和密码
$username=$_POST['username'];
$password=$_POST['password'];

//过滤用户输入数据
$username=mysqli_real_escape_string($con,strip_tags($username));
$password=mysqli_real_escape_string($con,strip_tags($password));

//构造SQL语句
$sql="SELECT * FROM users WHERE username='".$username."' AND password='".$password."'";

//执行SQL语句
$result=mysqli_query($con,$sql);

// 输出查询结果
while($row=mysqli_fetch_array($result,MYSQLI_ASSOC)){
    echo $row['username']. " " . $row['password'];
}

//关闭数据库连接
mysqli_close($con);
?>

In the above code, we use the functions mysqli_real_escape_string() and strip_tags() to filter user input data and ensure its security.

3. Summary

SQL injection attack is a common security problem in web applications, which can cause immeasurable losses to the database and user data. In order to avoid SQL injection attacks, we should ensure the accuracy of input data, filter user input data, use parameterized queries and other methods to strengthen the security of web applications. As developers, we need to constantly learn and understand the latest security technologies to ensure the security of web applications.

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