什么是文件上传漏洞？

黑客利用文件上传后服务器解析处理文件的漏洞上传一个可执行的脚本文件，并通过此脚本文件获得了执行服务器端命令的能力。

造成文件上传漏洞的原因:

1.服务器配置不当

2.开源编辑器上传漏洞

3.本地文件上传限制被绕过

4.过滤不严格被绕过

5.文件解析漏洞导致文件执行

6.文件路径截断

pikachu靶场-Unsafe Upfileupload_打开pikachu平台中的 unsafe upfileupload 客户端check,上传其他格式文-CSDN博客具体操作请看这篇文章

low等级

<?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
		$html .= '<pre>Your image was not uploaded.</pre>';
	}
	else {
		// Yes!
		$html .= "<pre>{$target_path} succesfully uploaded!</pre>";
	}
}

?>

php basename()函数给出一个包含有指向一个文件的全路径的字符串，本函数返回基本的文件名。 

只是实现一个，无任何过滤和验证，直接上传文件即可

medium等级

<?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
			$html .= '<pre>Your image was not uploaded.</pre>';
		}
		else {
			// Yes!
			$html .= "<pre>{$target_path} succesfully uploaded!</pre>";
		}
	}
	else {
		// Invalid file
		$html .= '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>';
	}
}

?>

 获取用户上传文件的名称、类型和大小信息。通过文件类型限定只能上传图片，限制了大小100000b。

抓包后修改后缀名即可绕过检测

high等级

<?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
			$html .= '<pre>Your image was not uploaded.</pre>';
		}
		else {
			// Yes!
			$html .= "<pre>{$target_path} succesfully uploaded!</pre>";
		}
	}
	else {
		// Invalid file
		$html .= '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>';
	}
}

?>

getimagesize() 函数用于获取图像大小及相关信息，成功返回一个数组，失败则返回 FALSE 并产生一条 E_WARNING 级的错误信息。

getimagesize() 函数将测定任何 GIF，JPG，PNG，SWF，SWC，PSD，TIFF，BMP，IFF，JP2，JPX，JB2，JPC，XBM 或 WBMP 图像文件的大小并返回图像的尺寸以及文件类型及图片高度与宽度。

move_uploaded_file（file,newlocal） 函数表示把给定的文件移动到新的位置

上传文件名为file.jpg，且文件内容为<?php @eval($_POST['hacker']);?>，此时页面将报错，显示上传失败，因为getimagesize()函数判断该文件不是有效的图片文件，所以需要在文件中加入文件头GIF89a。

也可制作图片马进行绕过（具体教程在pikachu靶场处已经写明）

impossible等级 

<?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!
			$html .= "<pre><a href='{$target_path}{$target_file}'>{$target_file}</a> succesfully uploaded!</pre>";
		}
		else {
			// No
			$html .= '<pre>Your image was not uploaded.</pre>';
		}

		// Delete any temp files
		if( file_exists( $temp_file ) )
			unlink( $temp_file );
	}
	else {
		// Invalid file
		$html .= '<pre>Your image was not uploaded. We can only accept JPEG or PNG images.</pre>';
	}
}

// Generate Anti-CSRF token
generateSessionToken();

?>

imagecreatefromjpeg(filename)： 从给定的文件或url中创建一个新的图片

imagejpeg(image,filename,quality)： 从image图像中以 filename 文件名创建一个jpeg的图片，参数quality可选，0-100 (质量从小到大)

imagedestroy(image)： 销毁图像

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，对上传的图片文件进行重新编码，以去除任何元数据在文件移动后，删除任何临时文件，确保不会留下无用文件，导致攻击者无法上传含有恶意脚本的文件。