What are the potential security risks when including external files in PHP based on user input?

When including external files in PHP based on user input, there is a risk of remote file inclusion attacks where an attacker could potentially execute malicious code on the server. To mitigate this risk, it is important to validate and sanitize user input before including any external files. 

// Validate and sanitize user input before including external files
$user_input = $_GET['file'];

// Check if the file exists in a predefined list of allowed files
$allowed_files = ['file1.php', 'file2.php', 'file3.php'];
if (in_array($user_input, $allowed_files)) {
    include($user_input);
} else {
    echo "Invalid file input";
}

Keywords

file inclusion user input security risks PHP external files

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