PHP security protection: preventing file inclusion vulnerabilities

With the popularity of the Internet and the emergence of various websites, security has become the most important part of the website development process. As a popular programming language, PHP is not only suitable for rapid development, but also widely used in various application fields, especially in the field of web development. However, many web applications still face security issues due to the existence of PHP file inclusion vulnerabilities. This article aims to explain how to avoid this vulnerability.

1. What is a file inclusion vulnerability?
   The file inclusion vulnerability means that when developers do not properly check the file names or paths that users pass to the program, attackers can inject malicious code into web applications. An attacker could exploit this vulnerability to access the file system, read sensitive files, and execute arbitrary code.
2. Measures to prevent file inclusion vulnerabilities
   To avoid this vulnerability, developers need to take the following precautions:

2.1. Prohibit users from directly accessing the application root directory
An attacker can discover exploitable vulnerabilities by accessing the application's root directory. Therefore, users should be prohibited from directly accessing the root directory of the application. Instead, the application should be placed in a separate folder and this folder configured in the web server.

2.2. Check user input
In applications, we often need to get some data from the user. To avoid security holes, we must validate and filter user input. Especially in the case of file inclusion, we must ensure that the user enters the correct file name or path.

2.3. Use absolute paths
Using absolute paths instead of relative paths can prevent attackers from exploiting file inclusion vulnerabilities to access files outside the application.

2.4. Only allow access to legal files
When using the file inclusion function, only allow access to files that should be accessed. Therefore, specify a whitelist and only allow access to files listed in this list.

2.5. Prevent access to sensitive files
When using the file inclusion function, you should avoid accessing sensitive files. For example, you can disable access to configuration files, log files, etc. within your application.

2.6. Check the existence and readability of the file
Before trying to access the file, you must ensure that the file exists and you should have sufficient permissions to read it. Especially in security-sensitive situations, we must ensure that programs only access necessary files.

3. Summary
   The file inclusion vulnerability is a common web application security vulnerability that allows an attacker to unknowingly access sensitive files. In order to protect web applications from attacks, developers must handle such vulnerabilities carefully, take appropriate measures, and avoid using dynamic file inclusion functions when developing and deploying web applications. This can simplify the development process and improve security. The precautions described in this article are relatively basic, but can help developers avoid many common file inclusion vulnerabilities.

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