How can PHP developers ensure that uploaded files are secure and do not pose a risk to the server?

PHP developers can ensure that uploaded files are secure by validating the file type, limiting the size of the uploaded file, and storing the file outside the web root directory to prevent direct access. Additionally, developers should sanitize the file name to prevent directory traversal attacks and use functions like `move_uploaded_file()` to move the file to a secure location. 

// Example code snippet to validate and move an uploaded file
if(isset($_FILES['file'])) {
    $targetDir = 'uploads/';
    $targetFile = $targetDir . basename($_FILES['file']['name']);
    
    // Validate file type
    $fileType = pathinfo($targetFile, PATHINFO_EXTENSION);
    if($fileType != 'jpg' && $fileType != 'png' && $fileType != 'pdf') {
        die('Invalid file type.');
    }
    
    // Limit file size
    if($_FILES['file']['size'] > 1000000) {
        die('File is too large.');
    }
    
    // Move uploaded file to secure location
    if(move_uploaded_file($_FILES['file']['tmp_name'], $targetFile)) {
        echo 'File uploaded successfully.';
    } else {
        echo 'Error uploading file.';
    }
}

Keywords

file upload PHP security server-side validation file type checking secure file handling

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