Discuss the principles, hazards and defense methods of PHP array bypass

In PHP programming, array is a very common and practical data type. In many scenarios, we use arrays to store, process, and transfer data. However, if we accidentally use it improperly, it may cause security risks, such as array bypass. This article will explore in detail the principles, hazards and defense methods of PHP array bypass.

1. What is array bypass?

Array bypass refers to using specific attack techniques to obtain specific values ​​or variables from a set of arrays to bypass certain restrictions or checks. Attackers usually use some special characters or syntax to operate on arrays in order to bypass them.

2. Array bypass in PHP

In PHP programming, the most common case of array bypass is to obtain parameter values ​​through super-global variables such as $_GET and $_POST. These parameter values ​​are usually passed as an array. Attackers can use some specific characters or attack techniques to manipulate these arrays to bypass some restrictions or checks.

Below we use an example to illustrate the principle of PHP array bypass.

Assume that the registration function of a website is like this:

(1) The user enters the user name and password on the registration page;

(2) Sends a registration request to the server, The server receives the user name and password;

(3) The server checks the format of the user name and password. If the format is correct, the user name and password are added to the database and jumps to the login page;

(4) If the format check fails, return to the registration page and prompt the user to re-enter.

The key part of the format checking code is as follows:

if (!preg_match('/^[a-zA-Z0-9_]+$/', $_POST['username'])) {
    echo '用户名格式不正确';
    return;
}

if (!preg_match('/^[a-zA-Z0-9_]+$/', $_POST['password'])) {
    echo '密码格式不正确';
    return;
}

The function of this code is to check whether the username and password only contain letters, numbers and underscores. If the requirements are not met, an error message will be returned. However, if the attacker sends a parameter that meets certain conditions, he can bypass the restrictions of this code and achieve the purpose of the attack.

For example, the attacker modifies the URL parameters and converts the requested parameters into an array form. If you add an underscore to the array, you can bypass the underscore matching rules in the regular expression:

http://www.example.com/register.php?username[0]=admin&username[1]=_&password=test123

In this way, the server will think that the parameter conforms to the rules when checking the user name, but in fact the attacker will The name is set to "admin_", successfully bypassing the regular expression restrictions.

3. Dangers of PHP array bypass

PHP array bypass may lead to the following security issues:

(1)SQL injection: An attacker can construct specific parameters by value, bypassing the server's input checking mechanism, causing SQL statements to be injected, thereby obtaining the user's sensitive information.

(2) Code injection: An attacker can bypass the server's code checking mechanism by constructing specific parameter values, causing malicious code to be injected, thereby attacking the system.

(3) Denial of service attack: An attacker can construct a large number of request parameters, causing server resources to be exhausted, thereby causing a denial of service attack.

(4) Other security issues: PHP array bypass may also cause other security issues, such as file inclusion, command execution, etc.

4. How to defend against PHP array bypass attacks

In order to defend against PHP array bypass attacks, we can take the following measures:

(1) Filter and restrict user input , to avoid special characters or syntax being injected into the array.

(2) Verify the array and reject illegal or abnormal parameter values.

(3) Turn on PHP’s strict mode and prohibit the use of unsafe functions and syntax.

(4) Use security frameworks, such as Laravel, Symfony, etc., with powerful defense mechanisms.

(5) Upgrade the server to the latest version so that known vulnerabilities and security issues can be fixed in a timely manner.

To sum up, PHP array bypass is a common security risk and requires special attention when writing PHP code. Only by strengthening security awareness and taking effective defensive measures can the security and stability of the website be protected.

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