Low:

源代码：

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<?php
if( isset( $_POST[ 'Upload' ] ) ) {
    // Where are we going to be writing to?
    $target_path  = DVWA_WEB_PAGE_TO_ROOT . "hackable/uploads/";   //上传文件的路径
    $target_path .= basename( $_FILES[ 'uploaded' ][ 'name' ] );   //文件路径=上文文件的路径+文件名
    // 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>";
    }
}
?>

关键函数：

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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。
如果上传成功，则会提示 路径+succesfully uploaded! 如果上传失败，则会提示 Your image was not uploaded。
我们可以写一句话木马 1.php ，上传

Medium:

源代码：

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<?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，服务器对上传文件的大小和类型做了限制。只允许上传小于 100000 字节并且文件type类型是image/jpeg或 image/png 的

方法一：抓包修改文件的type

因为这里过滤的是文件的上传类型，而不是文件的后缀名

方法二：00截断

在php版本小于5.3.4的服务器中，当Magic_quote_gpc选项为off时，可以在文件名中使用%00截断

先上传一个木马，抓包：

修改后发送：

getmuma. php中的空格的16进制为20，需把他改为00

High:

源代码：

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<?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_ext  = substr( $uploaded_name, strrpos( $uploaded_name, '.' ) + 1); 
    $uploaded_size = $_FILES[ 'uploaded' ][ 'size' ]; 
    $uploaded_tmp  = $_FILES[ 'uploaded' ][ 'tmp_name' ]; 
    // Is it an image? 
    if( ( strtolower( $uploaded_ext ) == "jpg" || strtolower( $uploaded_ext ) == "jpeg" || strtolower( $uploaded_ext ) == "png" ) && 
        ( $uploaded_size < 100000 ) && 
        getimagesize( $uploaded_tmp ) ) { 
        // Can we move the file to the upload folder? 
        if( !move_uploaded_file( $uploaded_tmp, $target_path ) ) { 
            // No 
            echo '<pre>Your image was not uploaded.</pre>'; 
        } 
        else { 
            // Yes! 
            echo "<pre>{$target_path} succesfully uploaded!</pre>"; 
        } 
    } 
    else { 
        // Invalid file 
        echo '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>'; 
    } 
} 
?>

关键函数：

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strtolower() : 函数把字符串转换为小写。

strrpos(string,find,start):函数返回字符串find在另一字符串string中最后一次出现的位置，如果没有找到字符串则返回false，可选参数start规定在何处开始搜索。

getimagesize(string filename) ：函数会通过读取文件头，返回图片的长、宽等信息，如果没有相关的图片文件头，函数会报错。

High级别的代码读取文件名中最后一个”.”后的字符串，期望通过文件名来限制文件类型，因此要求上传文件名形式必须是”.jpg”、”.jpeg”、”.png”之一。同时，getimagesize函数更是限制了上传文件的文件头必须为图像类型

因为上传的文件为图片类型，因此服务器将上传的文件解析成图片文件，所以若向其发送请求时，服务器只会返回这个“图片”文件，并不会执行相应命令。这里可以借助Medium级别的文件包含漏洞来获取webshell权限，具体文件包含的方法可参考(Upload-labs)https://ddstick.github.io/2019/07/31/Upload-labs/#Pass-13-%E5%9B%BE%E7%89%87%E9%A9%AC

方法二：
采用%00截断的方法可以轻松绕过文件名的检查，但是需要将上传文件的文件头伪装成图片，且只能在php版本小于5.3.4的服务器中

Impossible

源代码：

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<?php 
 
if( isset( $_POST[ 'Upload' ] ) ) { 
    // Check Anti-CSRF token 
    checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' ); 
    // File information 
    $uploaded_name = $_FILES[ 'uploaded' ][ 'name' ]; 
    $uploaded_ext  = substr( $uploaded_name, strrpos( $uploaded_name, '.' ) + 1); 
    $uploaded_size = $_FILES[ 'uploaded' ][ 'size' ]; 
    $uploaded_type = $_FILES[ 'uploaded' ][ 'type' ]; 
    $uploaded_tmp  = $_FILES[ 'uploaded' ][ 'tmp_name' ]; 
    // Where are we going to be writing to? 
    $target_path   = DVWA_WEB_PAGE_TO_ROOT . 'hackable/uploads/'; 
    //$target_file   = basename( $uploaded_name, '.' . $uploaded_ext ) . '-'; 
    $target_file   =  md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext; 
    $temp_file     = ( ( ini_get( 'upload_tmp_dir' ) == '' ) ? ( sys_get_temp_dir() ) : ( ini_get( 'upload_tmp_dir' ) ) ); 
    $temp_file    .= DIRECTORY_SEPARATOR . md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext; 
    // Is it an image? 
    if( ( strtolower( $uploaded_ext ) == 'jpg' || strtolower( $uploaded_ext ) == 'jpeg' || strtolower( $uploaded_ext ) == 'png' ) && 
        ( $uploaded_size < 100000 ) && 
        ( $uploaded_type == 'image/jpeg' || $uploaded_type == 'image/png' ) && 
        getimagesize( $uploaded_tmp ) ) { 
        // Strip any metadata, by re-encoding image (Note, using php-Imagick is recommended over php-GD) 
        if( $uploaded_type == 'image/jpeg' ) { 
            $img = imagecreatefromjpeg( $uploaded_tmp ); 
            imagejpeg( $img, $temp_file, 100); 
        } 
        else { 
            $img = imagecreatefrompng( $uploaded_tmp ); 
            imagepng( $img, $temp_file, 9); 
        } 
        imagedestroy( $img ); 
        // Can we move the file to the web root from the temp folder? 
        if( rename( $temp_file, ( getcwd() . DIRECTORY_SEPARATOR . $target_path . $target_file ) ) ) { 
            // Yes! 
            echo "<pre><a href='${target_path}${target_file}'>${target_file}</a> succesfully uploaded!</pre>"; 
        } 
        else { 
            // No 
            echo '<pre>Your image was not uploaded.</pre>'; 
        } 
        // Delete any temp files 
        if( file_exists( $temp_file ) ) 
            unlink( $temp_file ); 
    } 
    else { 
        // Invalid file 
        echo '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>'; 
    } 
} 
// Generate Anti-CSRF token 
generateSessionToken(); 
?>

关键函数：

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in_get(varname)：函数返回相应选项的值

imagecreatefromjpeg ( filename ) ：函数返回图片文件的图像标识，失败返回false

imagejpeg ( image , filename , quality) ：从image图像以filename为文件名创建一个JPEG图像，可选参数quality，范围从 0（最差质量，文件更小）到 100（最佳质量，文件最大）。

imagedestroy( img ) ： 函数销毁图像资源

getchwd() 函数返回当前工作目录

可以看到，Impossible级别的代码对上传文件进行了重命名（为md5值，导致%00截断无法绕过过滤规则），加入Anti-CSRF token防护CSRF攻击，同时对文件的内容作了严格的检查，导致攻击者无法上传含有恶意脚本的文件

web安全之token和CSRF攻击https://blog.csdn.net/qq_15096707/article/details/51307024