What are the potential security risks of trying to access and read links from external folders in PHP?

Attempting to access and read links from external folders in PHP can pose security risks such as directory traversal attacks, where an attacker could potentially access sensitive files on the server. To mitigate this risk, it is important to sanitize user input and validate file paths before attempting to access them. One way to do this is by using the realpath() function to get the absolute path of the file and ensure that it is within the allowed directory.

// Sanitize and validate file path
$filePath = realpath($_GET['file']);

// Check if file path is within allowed directory
$allowedDirectory = '/path/to/allowed/directory/';
if (strpos($filePath, $allowedDirectory) !== 0) {
    die('Access denied');
}

// Access and read file
$fileContent = file_get_contents($filePath);
echo $fileContent;