What are the potential security risks of allowing external file inclusions in PHP?

Allowing external file inclusions in PHP can lead to security risks such as remote code execution, where an attacker can inject malicious code into the included file and execute it on the server. To mitigate this risk, it is recommended to validate and sanitize user input before including any external files.

// Validate and sanitize user input before including external files
$file = isset($_GET['file']) ? $_GET['file'] : 'default.php';
$file = basename($file); // Sanitize input by only allowing basic file names
include 'path/to/files/' . $file;