PHP SQL injection vulnerabilities and prevention measures

What is PHP SQL injection vulnerability?

In the development of many websites, using PHP and MySQL is the most common solution. Although PHP is very portable and easy to use, MySQL is also a completely free database. Their combination can generally quickly and easily develop websites full of various functions.

However, it should be noted that there is a potential security risk when using PHP and MySQL for development, which is SQL injection vulnerability.

SQL injection vulnerability refers to the behavior of attackers taking advantage of vulnerabilities in the website to splice some unintentional SQL statements into the original SQL statements, thereby causing the database to store, delete or modify data. Through this method, attackers can obtain a lot of sensitive information in the database, such as account passwords, bank card information, user permissions, etc.

Why do PHP SQL injection vulnerabilities appear?

Before learning about SQL injection vulnerabilities in depth, we need to first understand how to use the PHP programming language:

Before a PHP program is used to operate a database, it usually needs to connect to the database and generate a connection object. . In PHP, if the application cannot generate SQL statements by itself, it must use the functions provided by PHP, such as mysql_query() or mysqli_query(), etc. The format is as follows:

mysqli_query(connection,query);

Among them, connection is the connection object, and query is the SQL query statement.

The root of the problem is that the mysqli_query() function in PHP does not strictly check the SQL statement, nor does it check the structure of the SQL statement, and the query parameters are not filtered and escaped correctly. At this time, if the attacker adds some malicious SQL statements to the query parameters, the semantics of the entire SQL command will change, thereby causing an attack.

How to prevent PHP SQL injection vulnerabilities?

1. Using prepared statements

Prepared statements means not splicing together the SQL statement to be executed and query parameters, but creating a prepared statement object. and takes the parameters as input to this object. This avoids SQL injection attacks.

The following is an example of a prepared statement:

$stmt = $conn -> prepare("SELECT * FROM users WHERE username = ? AND password = ?");
$stmt -> bind_param("ss", $username, $password);
$stmt -> execute();

In the above code, the variable $stmt stores the created prepared statement object. The way to modify query parameters is to use the bind_param() function, so that injection attacks can be avoided.

2. Filter the input

Before adding the data entered by the user to the SQL statement, be sure to filter and escape the data correctly to avoid They become part of the malicious SQL command.

Filtering methods include removing and replacing special characters and escaping them using PHP functions to remove the possibility of injection attacks.

The following is an example of filtering:

$filtered_username =filter_var($username , FILTER_SANITIZE_STRING);
$filtered_password = filter_var($password , FILTER_SANITIZE_STRING);

The filter_var() function in the above code will remove any HTML tags and special characters from $username and $patssword and return a harmless character string.

3. Handling error messages

Sometimes a SQL injection attack may cause the application to crash. To avoid this situation, error messages need to be handled appropriately.

For example, you can write error messages to the log or send an email to the administrator so that the application can be fixed in a timely manner.

Summary

PHP SQL injection vulnerability is a common web application security vulnerability. This needs to be taken seriously and appropriate precautions taken to avoid attacks and data breaches. Although the above measures cannot completely prevent all attacks that exploit SQL injection vulnerabilities, efficient and conventional filtering and processing methods can reduce the risk of attacks and effectively protect network security.

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