Medien nur für eingeloggte Benutzer freigeben

# require login for media files
# more info: https://m0n.co/11
<IfModule mod_rewrite.c>
RewriteCond %{REQUEST_FILENAME} (.*)
RewriteCond %{HTTP_COOKIE} !wordpress_logged_in_([a-zA-Z0-9_]*) [NC]
      RewriteRule .* - [QSA,NC,L, R=301]
</IfModule>

Open up your .htaccess found on the root folder of your website then place the block of code bellow:

RewriteCond %{REQUEST_FILENAME} -s
RewriteRule ^wp-content/uploads/(.*)$ dl-file.php?file=$1 [QSA,L]

What the code above does is it detects if a file is being accessed directly under wp-content/uploads/ folder, we then redirect the user to dl-file.php to validate if the user has any privilege to view the file.

Now, create the file dl-file.php in your root directory then place the block of code bellow:

/*
* dl-file.php
*
* Protect uploaded files with login.
*
* @link http://wordpress.stackexchange.com/questions/37144/protect-wordpress-uploads-if-user-is-not-logged-in
*
* @author hakre <http://hakre.wordpress.com/>
* @license GPL-3.0+
* @registry SPDX
*/
 
require_once('wp-load.php');

is_user_logged_in() ||  auth_redirect();

list($basedir) = array_values(array_intersect_key(wp_upload_dir(), array('basedir' => 1)))+array(NULL);

$file =  rtrim($basedir,'/').'/'.str_replace('..', '', isset($_GET[ 'file' ])?$_GET[ 'file' ]:'');
if (!$basedir || !is_file($file)) {
  status_header(404);
  die('404 &#8212; File not found.');
}

$mime = wp_check_filetype($file);
if( false === $mime[ 'type' ] && function_exists( 'mime_content_type' ) )
  $mime[ 'type' ] = mime_content_type( $file );

if( $mime[ 'type' ] )
  $mimetype = $mime[ 'type' ];
else
  $mimetype = 'image/' . substr( $file, strrpos( $file, '.' ) + 1 );

header( 'Content-Type: ' . $mimetype ); // always send this
if ( false === strpos( $_SERVER['SERVER_SOFTWARE'], 'Microsoft-IIS' ) )
  header( 'Content-Length: ' . filesize( $file ) );

$last_modified = gmdate( 'D, d M Y H:i:s', filemtime( $file ) );
$etag = '"' . md5( $last_modified ) . '"';
header( "Last-Modified: $last_modified GMT" );
header( 'ETag: ' . $etag );
header( 'Expires: ' . gmdate( 'D, d M Y H:i:s', time() + 100000000 ) . ' GMT' );

// Support for Conditional GET
$client_etag = isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) ? stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) : false;

if( ! isset( $_SERVER['HTTP_IF_MODIFIED_SINCE'] ) )
  $_SERVER['HTTP_IF_MODIFIED_SINCE'] = false;

$client_last_modified = trim( $_SERVER['HTTP_IF_MODIFIED_SINCE'] );
// If string is empty, return 0. If not, attempt to parse into a timestamp
$client_modified_timestamp = $client_last_modified ? strtotime( $client_last_modified ) : 0;

// Make a timestamp for our most recent modification...
$modified_timestamp = strtotime($last_modified);

if ( ( $client_last_modified && $client_etag )
  ? ( ( $client_modified_timestamp >= $modified_timestamp) && ( $client_etag == $etag ) )
  : ( ( $client_modified_timestamp >= $modified_timestamp) || ( $client_etag == $etag ) )
  ) {
  status_header( 304 );
  exit;
}

// If we made it this far, just serve the file
readfile( $file );

To prevent direct access to directory listings, simply add the additional code bellow:

Options All -Indexes

Redirect to login page instead of showing Error Message 403 (Forbidden)

ErrorDocument 403 /login.php