PHP security protection: strengthen directory permission control

In Web development, directories are an important part of providing the resources required by Web applications. However, if the file directory access permissions are improper, it can easily cause Web security problems. For example, an unauthorized third party can upload malicious files to your server, causing the server to be attacked. Therefore, during the development process of web applications, directory permission control must be strengthened to prevent illegal access and malicious file uploads.

In order to strengthen directory permission control, we can take the following measures:

1. Restrict directory access permissions

In Linux systems, you can use the chmod command to Control directory permissions. The specific command is as follows:

chmod 700 /var/www/html/uploads/

The meaning of the above command is that only the directory owner (usually the Web server process) has the permission to access, write and execute the directory, and others do not have access permission.

2. Prohibit execution of script files

Some directories are used to store script files, such as PHP script files, which can be executed by the Web server process. If the web server process is compromised, this directory may be used to store and execute malicious scripts. To prevent this from happening, we can disable the execution of script files in the directory through the Apache configuration file. The specific method is as follows:

In the Apache configuration file, find the following code:

<Directory /var/www/html/>
    Options Indexes FollowSymLinks
    AllowOverride None
    Require all granted
</Directory>

Modify it to:

<Directory /var/www/html/>
    Options Indexes FollowSymLinks
    AllowOverride None
    Require all granted
    AddHandler txt .txt
    AddHandler html .html
    AddHandler htm .htm
    AddHandler php .php .inc
</Directory>

<FilesMatch ".(php|inc)$">
    Order Deny,Allow
    Deny from all
</FilesMatch>

In the above configuration file, we added some MIME types that enable the Apache server to serve HTML, TXT, and PHP files. Then, by matching PHP and INC file names in the tag, we disable execution of PHP and INC files in all directories.

3. Preventing file upload vulnerabilities

In some web applications, users can upload pictures, documents and other files. However, these uploaded files may contain malicious code, and attackers exploit payload file upload vulnerabilities to transmit malicious files to the server. In order to prevent attacks, we can enhance the security of file uploads through the following methods:

• Restrict the types of uploaded files.
  Only safe file types are allowed to be uploaded, such as pictures, documents, audio, etc. Dangerous file types are not allowed to be uploaded, such as EXE, BAT, DLL and other files.
• Filter uploaded files.
  Filter uploaded files to ensure the security of uploaded files. You can use third-party plug-ins or open source tools to check whether uploaded files contain malicious code.
• Store uploaded files in a secure directory.
  Store the uploaded file in a secure directory so that the web server does not have permission to execute the uploaded file. At the same time, it can also prevent the execution of malicious files transmitted by exploiting file upload vulnerabilities.

In general, when developing Web applications, strengthening directory permission control is an important means to defend against Web attacks. By reasonably and strictly controlling the access permissions of file directories, malicious behaviors can be effectively reduced. Directory permission control is a necessary prerequisite for Web security, and both programmers and managers should pay attention to it.

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