upload-lab针对在CTF中常见的20种文件上传漏洞进行总结

现在将一一讲解一下20种绕过方法
先放上黑盒测试情况下的思路图：

0x01 (1)本地js绕过

第一题使用JavaScript脚本进行过滤，我们可以通过浏览器中禁用JavaScript脚本施行绕过

或者通过burp抓包，上传一句话木马图，抓包，然后修改filename实现绕过。

0x02 各种后缀的绕过

(2)MIME类型检查

观察源码：

<?php
$is_upload = false;
$msg = null;
if (isset($_POST['submit'])) {
    if (file_exists(UPLOAD_PATH)) {
        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;
            } else {
                $msg = '上传出错！';
            }
        } else {
            $msg = '文件类型不正确，请重新上传！';
        }
    } else {
        $msg = UPLOAD_PATH.'文件夹不存在,请手工创建！';
    }
}

?>

这里是对content type进行检查，然后有两种方法实现绕过
（1）上传木马图，修改其filename的后缀为php。
（2）上传一句话木马，然后修改其content type 为 image/jpeg 。

(3)php类型绕过

可以尝试将filename的后缀名.php修改为.php5,.php3,.phtml
同样地使用burp抓包进行绕过。
不过这里要修改apache的httpd.conf文件

1	AddType application/x-httpd-php .php .phtml .phps .php5 .pht

不然会出现apache无法解析其他版本的php文件

(4)上传.htaccess文件绕过

根据提示：

然后发现.htaccess文件未被过滤，所以编写.htaccess文件,这里的yjh.jpg是我们的木马图

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<FilesMatch "yjh.jpg">
SetHandler application/x-httpd-php
</FilesMatch>

然后上传.htaccess文件，以及yjh.jpg
输入url:127.0.0.1/upload-lab/upload/yjh.jpg。
然后在我们打开这个文件时，将以php的形式打开，然后连接菜刀，获得shell

(5)对大小写的绕过

观察源码：

<?php
$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！';
    }
}
?>

发现这里对于大小写没有过滤，所以burp抓包修改其filename的后缀名.php为.PhP。如此，完成绕过。

(6)空格绕过

这一关的源码和第五关的源码差了

1	$file_ext = trim($file_ext); //首尾去空

所以我们在后缀名后加上空格，实现绕过。

绕过完成

(7)点号绕过

观察源码，发现这一关与第六关相比，少了如下代码：

1	$file_name = deldot($file_name);//删除文件名末尾的点

所以使用点号绕过，后缀名.php修改问.php.

(8)::$DATA绕过

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

所以一样的套路，后缀名由.php修改为.php::$DATA

(9)点号绕过2

关键代码：

$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

由于这段代码中的

1	$file_name = deldot($file_name);//删除文件名末尾的点

并不是递归删点，所以这里点号仅被删除了一次，然后我们可以通过双写点号实现绕过，修改”.php”为”.php. .”

(10)双写后缀名绕过

关键代码：

$file_name = str_ireplace($deny_ext,"", $file_name);

这说明这里的后缀名在过滤时也仅过滤了一次而已，所以我们修改”.php”为”.pphphp”实现绕过

(11)%00截断

%00截断-get型

观察源码：

<?php
$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！";
    }
}
?>

可以发现，这里已经使用白名单过滤
我们尝试抓包

可见save_path可控，于是构造save_path=../upload/shell.php%00
修改filename=”shell.jpg”

实现绕过

%00截断-post型

由于post无法对%00自动解码，所以我们使用burp的decorder模块修改hex20为00

完成绕过