uplload 通关纪实 pass6

Posted 2022-12-12 安全界 的彭于晏

这一关将htaccess也ban了。
大小写绕过原理：
Windows系统下，对于文件名中的大小写不敏感。例如：test.php和TeSt.PHP是一样的。
Linux系统下，对于文件名中的大小写敏感。例如：test.php和 TesT.php就是不一样的。
去除对文件后缀名的转为小写设定，可以直接选择后缀名为.PHp等非黑名单中存在的格式上传。
同样也可以抓包到repeater模块修改文件后缀名为.PHp等等非黑名单中存在的格式上传。

源代码如下：

$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",".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

        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！';
    

先上传一个php文件，用burpsuite抓包：

之后发送到repeater模块，修改文件后缀名为.PHp，点击Go，可以看到成功上传，文件名也发生了改变：

用菜刀进行连接：

成功访问到该文件的目录：