文章目录
- low等级
- medium等级
- high等级
- Impossible等级
low等级
查看源码：
<?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' ] );
// 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>";
}
}
?>
对上传的文件没有任何过滤，上传一个具有一句话木马的php文件：
上传成功，并且返回成功的地址：
medium等级
做代码审计：
<?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>';
}
}
?>
发现它是接收了一个http头部，并用post方法传参，并在
if(($uploaded_type == "image/jpeg" || $uploaded_type == "image/png") && ($uploaded_size < 100000))
限制了接收文件的类型，即只接收jpeg、png格式的图片，并限制了上传文件的大小不能超过100k。
我们继续上传有一句话木马的php文件，然后用bp抓包，修改文件的类型字段为image/png：
点击放包后可以看到上传文件成功：
high等级
查看源码：
<?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_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>';
}
}
在代码中有
$uploaded_ext = substr( $uploaded_name, strrpos($uploaded_name, '.') + 1);
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( $uploaded_tmp)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则报错
这段代码在medium的基础上增加了读取文件头，判断文件幻数来更严格地判断文件的类型，提高了过滤的强度。
接下来我们准备一张图片和包含一句话木马的php文件：
用下面的命令将它们合并成一个新的图片：
copy dvwa_email.jpg/b + 1.php/a 2.jpg
然后直接上传，网页提示上传成功：
Impossible等级
查看源码，做代码审计：
<?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();
?>
发现这段代码包含了high等级的过滤策略，会检查图片文件的头部，用幻数来更严格地判断文件的类型，不仅如此，它还在
if( $uploaded_type == 'image/jpeg' ) {
$img = imagecreatefromjpeg( $uploaded_tmp );
imagejpeg( $img, $temp_file, 100);
}
else {
$img = imagecreatefrompng( $uploaded_tmp );
imagepng( $img, $temp_file, 9);
}
中用imagecreatefromjpeg( $uploaded_tmp )函数对上传的图片进行二次渲染，相当于直接生成一个外观相同的新图片文件，这样一来，如果图片中存在恶意代码，就会被过滤，这中方式更严密地防范了漏洞，导致攻击者无法上传木马文件。
