File Upload
文件上传漏洞,通常是由于对上传文件的类型、内容没有进行严格的过滤、检查,使得攻击者可以通过上传木马获取服务器的webshell权限,因此文件上传漏洞带来的危害常常是毁灭性的,Apache、Tomcat、Nginx等都曝出过文件上传漏洞
low
<?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>";
}
}
?>
文件上传漏洞的利用是有限制条件的,首先当然是要能够成功上传木马文件,其次上传文件必须能够被执行,最后就是上传文件的路径必须可知。不幸的是,这里三个条件全都满足
上传一句话木马
构造url如下
http://127.0.0.1/DVWA-master/hackable/uploads/1.php
菜刀可以直接连接上
medium
<?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,Medium级别的代码对上传文件的类型、大小做了限制,要求文件类型必须是jpeg或者png,大小不能超过100000B(约为97.6KB)
把一句话木马1.php改成1.jpg,发现上传成功,中国菜刀的原理是向上传文件发送包含apple参数的post请求,通过控制apple参数来执行不同的命令,而这里服务器将木马文件解析成了图片文件,因此向其发送post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
法一
文件包含+文件上传
图片为php文件改后缀的jpg文件,构造如下url(中级的文件包含对http过滤,采取双写绕过),浏览网页
http://127.0.0.1/DVWA-master/vulnerabilities/fi/?page=hthttp://tp://127.0.0.1/DVWA-master/hackable/uploads/123.jpg
将后面的都删除,留下http://127.0.0.1/DVWA-master/
点击浏览,输入DVWA账号密码,退出后保存cookie
连接成功
法二
burpsuit修改后缀(先打开一个由php文件改后缀的jpg文件)
把1.jpg修改为1.php,还原文件
把Content-Type: application/octet-stream修改为Content-Type: image/png
构造url
http://127.0.0.1/DVWA-master/hackable/uploads/1.php
都能连接成功
high
核心代码如下:
<?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>';
}
}
?>
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。
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。
copy a.png/b+b.php/a c.png //图片是二进制,php是文本
会生成一个png文件,在这个png文件末尾有php代码
蚁剑地址中输入如下url
http://127.0.0.1/DVWA-master/
先连接浏览网站,存一下cookie,然后再编辑一下网址为
http://127.0.0.1/DVWA-master/vulnerabilities/fi/?page=file:///C:phpStudy/PHPTutorial/WWW/DVWA-master/hackable/uploads/hack.jpg
连接成功
impossible
<?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();
?>
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
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。