DVWA靶场通关----(5) File Upload教程

File Upload（文件上传）

File Upload（文件上传），由于对上传文件的内、类型没有做严格的过滤、检查，使得攻击者可以通过上传木马文件获取服务器的webshell文件。

File Upload主题：

 

Low

源码解析

<?php

if( isset( $_POST[ 'Upload' ] ) ) {
    // Where are we going to be writing to?
//文件的目标路径hackable/uploads/，也就是文件上传的位置
    $target_path  = DVWA_WEB_PAGE_TO_ROOT . "hackable/uploads/";
// 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。
    $target_path .= basename( $_FILES[ 'uploaded' ][ 'name' ] );

    // Can we move the file to the upload folder?
//移动用户上传文件至目标路径
    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>";
    }
}

?>

漏洞复现

　　从源码中可以看到对上传文件的类型、内容没有做任何的过滤与检查，同时告诉了我们文件上传的路径，存在明显的文件上传漏洞。

（1）上传一个phpinfo.php进行测试

 当我们上传成功后，会提示我们成功上传，并且返回一个上传文件的路径

（2）打开我们所上传的文件

 

Medium

源码解析

<?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?
//文件类型必须是image/jpeg 或者 image/png，大小不能超过100000B（约为97.6KB）
    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>';
    }
}

?>

　　对文件上传的类型做了限制，要求必须是image/jpeg 或者 image/png 类型的。

漏洞复现

（1）还是使用刚才的phpinfo.php（把刚才上传的那个记得删掉）

 

 （2）打开上传的文件

 

High

源码解析

<?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?
// strtoLower把所有字符转换为小写
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。
可以看到，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。
    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>';
    }
}

?>

　　这个就必须上传一个图片马了，他对文件的文件头，文件名形式等等都做了检查。

漏洞复现

（1）先制作一个图片马（注意：图片马的文件大小不能超过100000B）

copy phpinfo.png/b+phpinfo.php/a phpinfo.png

 

 （2）将准备好的图片马上传

 （3）打开上传的图片马，可以看到上传成功

 （4）结合文件包含漏洞，去包含我们上传的文件，成功执行phpinfo

 

Impossible

源码解析

<?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 ) . '-';
//上传文件的文件前缀md5加密
    $target_file   =  md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext;
//in_get(varname)
函数返回相应选项的值
    $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' ) {
//imagecreatefromjpeg ( filename )
函数返回图片文件的图像标识，失败返回false
            $img = imagecreatefromjpeg( $uploaded_tmp );
//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）。
            imagejpeg( $img, $temp_file, 100);
        }
        else {
            $img = imagecreatefrompng( $uploaded_tmp );
            imagepng( $img, $temp_file, 9);
        }
// imagedestroy( img )
函数销毁图像资源
        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();

?>

漏洞复现

　　这个级别的文件上传对上传的文件进行了重命名（搞了一个MD5的加密），还增加了token值的校验，对文件的内容也做了严格的检查。