public function SecurityFileUploadEventSubscriber::sanitizeName in Drupal 9

Sanitizes the upload's filename to make it secure.

Parameters

\Drupal\Core\File\Event\FileUploadSanitizeNameEvent $event: File upload sanitize name event.

File

core/modules/system/src/EventSubscriber/SecurityFileUploadEventSubscriber.php, line 50

Class

SecurityFileUploadEventSubscriber

The final subscriber to 'file.upload.sanitize.name'.

Namespace

Drupal\system\EventSubscriber

Code

public function sanitizeName(FileUploadSanitizeNameEvent $event) : void {
  $filename = $event
    ->getFilename();

  // Dot files are renamed regardless of security settings.
  $filename = trim($filename, '.');

  // Remove any null bytes. See
  // http://php.net/manual/security.filesystem.nullbytes.php
  $filename = str_replace(chr(0), '', $filename);

  // Split up the filename by periods. The first part becomes the basename,
  // the last part the final extension.
  $filename_parts = explode('.', $filename);

  // Remove file basename.
  $filename = array_shift($filename_parts);

  // Remove final extension.
  $final_extension = (string) array_pop($filename_parts);
  $extensions = $event
    ->getAllowedExtensions();
  if (!empty($extensions) && !in_array(strtolower($final_extension), $extensions, TRUE)) {

    // This upload will be rejected by file_validate_extensions() anyway so do
    // not make any alterations to the filename. This prevents a file named
    // 'example.php' being renamed to 'example.php_.txt' and uploaded if the
    // .txt extension is allowed but .php is not. It is the responsibility of
    // the function that dispatched the event to ensure file_validate() is
    // called with 'file_validate_extensions' in the list of validators if
    // $extensions is not empty.
    return;
  }
  if (!$this->config
    ->get('allow_insecure_uploads') && in_array(strtolower($final_extension), FileSystemInterface::INSECURE_EXTENSIONS, TRUE)) {
    if (empty($extensions) || in_array('txt', $extensions, TRUE)) {

      // Add .txt to potentially executable files prior to munging to help prevent
      // exploits. This results in a filenames like filename.php being changed to
      // filename.php.txt prior to munging.
      $filename_parts[] = $final_extension;
      $final_extension = 'txt';
    }
    else {

      // Since .txt is not an allowed extension do not rename the file. The
      // file will be rejected by file_validate().
      return;
    }
  }

  // If there are any insecure extensions in the filename munge all the
  // internal extensions.
  $munge_everything = !empty(array_intersect(array_map('strtolower', $filename_parts), FileSystemInterface::INSECURE_EXTENSIONS));

  // Munge the filename to protect against possible malicious extension hiding
  // within an unknown file type (i.e. filename.html.foo). This was introduced
  // as part of SA-2006-006 to fix Apache's risky fallback behaviour.
  // Loop through the middle parts of the name and add an underscore to the
  // end of each section that could be a file extension but isn't in the
  // list of allowed extensions.
  foreach ($filename_parts as $filename_part) {
    $filename .= '.' . $filename_part;
    if ($munge_everything) {
      $filename .= '_';
    }
    elseif (!empty($extensions) && !in_array(strtolower($filename_part), $extensions) && preg_match("/^[a-zA-Z]{2,5}\\d?\$/", $filename_part)) {
      $filename .= '_';
    }
  }
  if ($final_extension !== '') {
    $filename .= '.' . $final_extension;
  }
  if ($filename !== $event
    ->getFilename()) {
    $event
      ->setFilename($filename)
      ->setSecurityRename();
  }
}