环境要求

若要自己亲自搭建环境，请按照以下配置环境，方可正常运行每个Pass。

第十六关

源码解读

$is_upload = false;
$msg = null;
if (isset($_POST['submit'])){
    // 获得上传文件的基本信息，文件名，类型，大小，临时文件路径
    $filename = $_FILES['upload_file']['name'];
    $filetype = $_FILES['upload_file']['type'];
    $tmpname = $_FILES['upload_file']['tmp_name'];

    $target_path=$UPLOAD_ADDR.basename($filename);

    // 获得上传文件的扩展名
    $fileext= substr(strrchr($filename,"."),1);

    //判断文件后缀与类型，合法才进行上传操作
    if(($fileext == "jpg") && ($filetype=="image/jpeg")){
        if(move_uploaded_file($tmpname,$target_path))
        {
            //使用上传的图片生成新的图片
            $im = imagecreatefromjpeg($target_path);

            if($im == false){
                $msg = "该文件不是jpg格式的图片！";
            }else{
                //给新图片指定文件名
                srand(time());
                $newfilename = strval(rand()).".jpg";
                $newimagepath = $UPLOAD_ADDR.$newfilename;
                imagejpeg($im,$newimagepath);
                //显示二次渲染后的图片（使用用户上传图片生成的新图片）
                $img_path = $UPLOAD_ADDR.$newfilename;
                unlink($target_path);
                $is_upload = true;
            }
        }
        else
        {
            $msg = "上传失败！";
        }

    }else if(($fileext == "png") && ($filetype=="image/png")){
        if(move_uploaded_file($tmpname,$target_path))
        {
            //使用上传的图片生成新的图片
            $im = imagecreatefrompng($target_path);

            if($im == false){
                $msg = "该文件不是png格式的图片！";
            }else{
                 //给新图片指定文件名
                srand(time());
                $newfilename = strval(rand()).".png";
                $newimagepath = $UPLOAD_ADDR.$newfilename;
                imagepng($im,$newimagepath);
                //显示二次渲染后的图片（使用用户上传图片生成的新图片）
                $img_path = $UPLOAD_ADDR.$newfilename;
                unlink($target_path);
                $is_upload = true;               
            }
        }
        else
        {
            $msg = "上传失败！";
        }

    }else if(($fileext == "gif") && ($filetype=="image/gif")){
        if(move_uploaded_file($tmpname,$target_path))
        {
            //使用上传的图片生成新的图片
            $im = imagecreatefromgif($target_path);
            if($im == false){
                $msg = "该文件不是gif格式的图片！";
            }else{
                //给新图片指定文件名
                srand(time());
                $newfilename = strval(rand()).".gif";
                $newimagepath = $UPLOAD_ADDR.$newfilename;
                imagegif($im,$newimagepath);
                //显示二次渲染后的图片（使用用户上传图片生成的新图片）
                $img_path = $UPLOAD_ADDR.$newfilename;
                unlink($target_path);
                $is_upload = true;
            }
        }
        else
        {
            $msg = "上传失败！";
        }
    }else{
        $msg = "只允许上传后缀为.jpg|.png|.gif的图片文件！";
    }
}

• 本关综合判断了后缀名、content-type，以及利用imagecreatefromgif判断是否为gif图片，最后再做了一次二次渲染

bypass

第十七关

源码解读

$is_upload = false;
$msg = null;

if(isset($_POST['submit'])){
    $ext_arr = array('jpg','png','gif');
    $file_name = $_FILES['upload_file']['name'];
    $temp_file = $_FILES['upload_file']['tmp_name'];
    $file_ext = substr($file_name,strrpos($file_name,".")+1);
    $upload_file = $UPLOAD_ADDR . '/' . $file_name;

    if(move_uploaded_file($temp_file, $upload_file)){
        // 先移动图片,有条件竞争的前提条件
        if(in_array($file_ext,$ext_arr)){
             $img_path = $UPLOAD_ADDR . '/'. rand(10, 99).date("YmdHis").".".$file_ext;
             rename($upload_file, $img_path);
             unlink($upload_file);
             $is_upload = true;
        }else{
            $msg = "只允许上传.jpg|.png|.gif类型文件！";
            unlink($upload_file);
        }
    }else{
        $msg = '上传失败！';
    }
}

• 这里先将文件上传到服务器，然后通过rename修改名称，再通过unlink删除文件，因此可以通过条件竞争的方式在unlink之前，访问webshell

bypass

首先在burp中不断发送上传webshell的数据包,然后不断在浏览器中访问，发现通过竞争可以访问到。

第十八关

源码解读

/index.php
$is_upload = false;
$msg = null;
if (isset($_POST['submit']))
{
    require_once("./myupload.php");
    $imgFileName =time();
    $u = new MyUpload($_FILES['upload_file']['name'], $_FILES['upload_file']['tmp_name'], $_FILES['upload_file']['size'],$imgFileName);
    $status_code = $u->upload($UPLOAD_ADDR);
    switch ($status_code) {
        case 1:
            $is_upload = true;
            $img_path = $u->cls_upload_dir . $u->cls_file_rename_to;
            break;
        case 2:
            $msg = '文件已经被上传，但没有重命名。';
            break; 
        case -1:
            $msg = '这个文件不能上传到服务器的临时文件存储目录。';
            break; 
        case -2:
            $msg = '上传失败，上传目录不可写。';
            break; 
        case -3:
            $msg = '上传失败，无法上传该类型文件。';
            break; 
        case -4:
            $msg = '上传失败，上传的文件过大。';
            break; 
        case -5:
            $msg = '上传失败，服务器已经存在相同名称文件。';
            break; 
        case -6:
            $msg = '文件无法上传，文件不能复制到目标目录。';
            break;      
        default:
            $msg = '未知错误！';
            break;
    }
}

//myupload.php
class MyUpload{
......
......
...... 
  var $cls_arr_ext_accepted = array(
      ".doc", ".xls", ".txt", ".pdf", ".gif", ".jpg", ".zip", ".rar", ".7z",".ppt",
      ".html", ".xml", ".tiff", ".jpeg", ".png" );

......
......
......  
  /** upload()
   **
   ** Method to upload the file.
   ** This is the only method to call outside the class.
   ** @para String name of directory we upload to
   ** @returns void
  **/
  function upload( $dir ){
    
    $ret = $this->isUploadedFile();
    
    if( $ret != 1 ){
      return $this->resultUpload( $ret );
    }

    $ret = $this->setDir( $dir );
    if( $ret != 1 ){
      return $this->resultUpload( $ret );
    }

    $ret = $this->checkExtension();
    if( $ret != 1 ){
      return $this->resultUpload( $ret );
    }

    $ret = $this->checkSize();
    if( $ret != 1 ){
      return $this->resultUpload( $ret );    
    }
    
    // if flag to check if the file exists is set to 1
    
    if( $this->cls_file_exists == 1 ){
      
      $ret = $this->checkFileExists();
      if( $ret != 1 ){
        return $this->resultUpload( $ret );    
      }
    }

    // if we are here, we are ready to move the file to destination

    $ret = $this->move();
    if( $ret != 1 ){
      return $this->resultUpload( $ret );    
    }

    // check if we need to rename the file

    if( $this->cls_rename_file == 1 ){
      $ret = $this->renameFile();
      if( $ret != 1 ){
        return $this->resultUpload( $ret );    
      }
    }
    
    // if we are here, everything worked as planned :)

    return $this->resultUpload( "SUCCESS" );
  
  }
......
......
...... 
};

• 需要上传一个图片mm
• 本关对文件后缀名做了白名单判断，然后会一步一步检查文件大小、文件是否存在等等

bypass

将文件上传后，对文件重新命名，同样存在条件竞争的漏洞。可以不断利用burp发送上传图片马的数据包，由于条件竞争，程序会出现来不及rename的问题，从而上传成功：

第十九关

源码解读

$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    if (file_exists($UPLOAD_ADDR)) {
        $deny_ext = array("php","php5","php4","php3","php2","html","htm","phtml","pht","jsp","jspa","jspx","jsw","jsv","jspf","jtml","asp","aspx","asa","asax","ascx","ashx","asmx","cer","swf","htaccess");

        $file_name = $_POST['save_name'];
        $file_ext = pathinfo($file_name,PATHINFO_EXTENSION);

        if(!in_array($file_ext,$deny_ext)) {
            $img_path = $UPLOAD_ADDR . '/' .$file_name;
            if (move_uploaded_file($_FILES['upload_file']['tmp_name'], $img_path)) { 
                $is_upload = true;
            }else{
                $msg = '上传失败！';
            }
        }else{
            $msg = '禁止保存为该类型文件！';
        }

    } else {
        $msg = $UPLOAD_ADDR . '文件夹不存在,请手工创建！';
    }
}

_POST['save_name'];中有变量可控 发现move_uploaded_file()函数中的img_path是由post参数save_name控制的，因此可以在save_name利用00截断绕过