How to avoid file inclusion vulnerability security issues in PHP language development?

PHP language has always been a popular web development language. It has simple and easy-to-read syntax, powerful functions and a huge ecosystem. In a large number of web applications, the PHP language plays an important role. However, when used inappropriately, it can become a vulnerable vulnerability, and file inclusion vulnerability is one of them. In this article, we will introduce the definition of file inclusion vulnerabilities and discuss how to avoid the security issues of file inclusion vulnerabilities as much as possible.

What is a file inclusion vulnerability?

The file inclusion vulnerability means that when a file is included through dynamic reference, unfiltered user-controlled input is passed directly to the file inclusion function, causing the attacker to bypass the file by controlling the file name or parameters. Failure to verify file names may ultimately lead to serious security issues such as attackers successfully injecting malicious code, obtaining system information, reading file contents, and remotely controlling the system. It can be seen that file inclusion vulnerabilities are very dangerous, and attackers can use this vulnerability to control the entire system.

How to avoid file inclusion vulnerabilities?

The key to avoiding file inclusion vulnerabilities lies in filtering user input parameters, which can be achieved through the following methods:

1. Specify the file path format

When using the web application framework, an application root directory is generally defined. The files in this directory are accessible to users. This directory is generally obtained through the $_SERVER['DOCUMENT_ROOT'] variable. When including files, you should use relative paths based on this directory instead of absolute paths, so that paths that may bypass security verification cannot be used by attackers.

2. Use the whitelist mechanism

Use the whitelist mechanism to clearly specify which files can be included and which files cannot be included. All user input parameters must be whitelisted first, and only legal files will be included.

3. Use the realpath function in PHP to get the absolute path of the file

If a dynamic variable based on the file name is used, the file path must be constructed based on the information provided by the user . So we must use the realpath function to get the absolute path of the file, and then determine whether the file is under the application path to prevent attackers from injecting content such as bytes/blog.php/../../etc/passwd into the foo variable. Thus gaining complete control over the system.

For example:

$file = $_REQUEST['file'];
if (!realpath('./'.$file)) {
    die('Invalid file path');
}

4. Use template engines such as twig and symfony in PHP 7 to render templates

Many functions of the template engine are based on predefined The path of these templates may be very restricted, so template rendering can be achieved by using template engines such as twig and symfony, thus greatly reducing the developer's work in processing input parameters.

Summary

File containing vulnerabilities can cause many network security problems and must be prevented and repaired. The key to avoiding file inclusion vulnerabilities is to strictly filter user-entered parameters and not rely solely on the user's credibility. Adopting a whitelist mechanism, file path formatting, and using template engines such as twig and symfony in PHP7 are all effective defense measures that can help us effectively prevent security issues where files contain vulnerabilities. Let us pay attention to security issues during the development process and build safe and reliable web applications.

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