How to prevent directory traversal attacks in PHP?

@darrion.kuhn 

Directory traversal attacks are a type of security vulnerability in web applications where an attacker can access files outside the intended directory. Here are some ways to prevent directory traversal attacks in PHP:

1. Input Validation: Always validate user input and sanitize user-supplied input data to ensure that it conforms to the expected format. Avoid using user input to construct file paths or include files directly without validating or sanitizing them.
2. Use Whitelist-based Input Validation: Use a whitelist-based input validation approach to only allow user-supplied input data that is explicitly allowed, rather than trying to blacklist all potentially malicious input.
3. Use Realpath Function: Use the realpath() function to resolve the full path of a file or directory, which can help prevent directory traversal attacks by ensuring that the requested file is located within the intended directory.
4. Restrict Access to Sensitive Directories: Restrict access to sensitive directories by using permissions and access controls to ensure that only authorized users have access to these directories.
5. Use Frameworks and Libraries: Use a reputable PHP framework or library that provides built-in security features to help prevent directory traversal attacks. Examples include Laravel, Symfony, and CodeIgniter.
6. Use Safe Path Function: Use the safe path function, such as basename(), which extracts the base name of a file or directory, to prevent directory traversal attacks.
7. Use a Web Application Firewall: Implement a web application firewall that can detect and block malicious requests, including directory traversal attacks.

By following these best practices, you can help prevent directory traversal attacks in your PHP applications and enhance their overall security.