文件上传本身不是漏洞,但如果文件上传功能的限制出现纰漏,允许了不合法且影响网站安全的文件的上传
可以将不合法且影响网站安全稳定性的文件等内容上传的均为“文件上传漏洞”
黑方将文件上传后可通过手段执行以及上传的脚本文件(通过获得上传的地址目录查看文件并达到目的)
一般的,以上所述的内容文件为通俗的所说的:“一句话木马”。
而文件上传功能是大多web应用均具备的功能(例如图片、附件、头像等)正常的将文件上传是合法的。
但如果通过修改文件性质,绕过web应用的限制,将恶意的脚本文件上传到服务器后台,并可以执行,意味着获得了webshell
获得webshell则意味着服务器的操作权限被拿到了下一步的攻击则是最危险的(违法)
{用户=是无法直接看见后端代码的,后端代码在服务器,当用户请求服务器
(静态下,由服务器给出响应,浏览器直接渲染)
(动态下,浏览器和后端的php中间件通信,由中间件对程序处理或解释,最终生成html的结果)}
流程:
成功上传——获得脚本路径——webshell
成功绕过机制将恶意脚本上传到服务器路径下后
获得脚本存放的路径
进入脚本存储路径对脚本执行(中国菜刀)
low等级:
没有任何审查机制,直接将php脚本上传即可上传成功并获得脚本位置后
1 <?php 2 3 if( isset( $_POST[ 'Upload' ] ) ) { 4 // Where are we going to be writing to? 5 $target_path = DVWA_WEB_PAGE_TO_ROOT . "hackable/uploads/"; 6 $target_path .= basename( $_FILES[ 'uploaded' ][ 'name' ] ); 7 8 // Can we move the file to the upload folder? 9 if( !move_uploaded_file( $_FILES[ 'uploaded' ][ 'tmp_name' ], $target_path ) ) {10 // No11 echo '<pre>Your image was not uploaded.</pre>';12 }13 else {14 // Yes!15 echo "<pre>{$target_path} succesfully uploaded!</pre>";16 }17 }18 19 ?>
{ps:实际情况下,用户是无法直接看见php源码和路径地址的}
Low等级的机制下没有对上传的文件类型进行检查,所以直接上传php脚本即可;会返回路径(靶机返回,现实中不直接返回)
Medium等级:
添加了对文件格式、大小的检查机制
1 if( isset( $_POST[ 'Upload' ] ) ) { 2 // Check Anti-CSRF token 3 checkToken( $_REQUEST[ 'user_token' ], $_SESSION[ 'session_token' ], 'index.php' ); 4 5 6 // File information 7 $uploaded_name = $_FILES[ 'uploaded' ][ 'name' ]; 8 $uploaded_ext = substr( $uploaded_name, strrpos( $uploaded_name, '.' ) + 1); 9 $uploaded_size = $_FILES[ 'uploaded' ][ 'size' ];10 $uploaded_type = $_FILES[ 'uploaded' ][ 'type' ];11 $uploaded_tmp = $_FILES[ 'uploaded' ][ 'tmp_name' ];12 13 // Where are we going to be writing to?14 $target_path = DVWA_WEB_PAGE_TO_ROOT . 'hackable/uploads/';15 //$target_file = basename( $uploaded_name, '.' . $uploaded_ext ) . '-';16 $target_file = md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext;17 $temp_file = ( ( ini_get( 'upload_tmp_dir' ) == '' ) ? ( sys_get_temp_dir() ) : ( ini_get( 'upload_tmp_dir' ) ) );18 $temp_file .= DIRECTORY_SEPARATOR . md5( uniqid() . $uploaded_name ) . '.' . $uploaded_ext;19 20 // Is it an image?21 if( ( strtolower( $uploaded_ext ) == 'jpg' || strtolower( $uploaded_ext ) == 'jpeg' || strtolower( $uploaded_ext ) == 'png' ) &&22 ( $uploaded_size < 100000 ) &&23 ( $uploaded_type == 'image/jpeg' || $uploaded_type == 'image/png' ) &&24 getimagesize( $uploaded_tmp ) ) {25 26 // Strip any metadata, by re-encoding image (Note, using php-Imagick is recommended over php-GD)27 if( $uploaded_type == 'image/jpeg' ) {28 $img = imagecreatefromjpeg( $uploaded_tmp );29 imagejpeg( $img, $temp_file, 100);30 }31 else {32 $img = imagecreatefrompng( $uploaded_tmp );33 imagepng( $img, $temp_file, 9);34 }35 imagedestroy( $img );36 37 // Can we move the file to the web root from the temp folder?38 if( rename( $temp_file, ( getcwd() . DIRECTORY_SEPARATOR . $target_path . $target_file ) ) ) {39 // Yes!40 echo "<pre><a href='${target_path}${target_file}'>${target_file}</a> succesfully uploaded!</pre>";41 }42 else {43 // No44 echo '<pre>Your image was not uploaded.</pre>';45 }46 47 // Delete any temp files48 if( file_exists( $temp_file ) )49 unlink( $temp_file );50 }51 else {52 // Invalid file53 echo '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>';54 }55 }56 57 // Generate Anti-CSRF token58 generateSessionToken();59 60 ?>
Medium等级下上传gif/jpg(MIME类型和后缀)且1000b以下的文件即可上传成功;除此以外的文件均被拦截不可上传。
而在安全领域下有一个名词:绕过(过狗)
通过Burp代理进行访问后拦击数据包并修改后释放上传
文件上传绕过思路:推荐文章
https://www.cnblogs.com/blacksunny/p/8001201.html
https://www.freebuf.com/articles/web/179954.html
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