Platform_强网24

CTF

分析与尝试

  1. 前端没有东西开扫，有www.zip
  2. 目标就是notous…中析构执行任意代码，问题就是访问不到有些难绷，序列化和反序列化？
    1. 需要从session入手，查查php seesion利用方式，发现有一个反序列化漏洞，看一看，差不多了解了
      1. session写入键供后续反序列化，生成notouc…对象，注意到每一次访问都会进行读取，5.5.4后默认php_serialize(复现看不到版本，但是看wp一部分是php方式)，使用竖线|来实现加载时的反序列化
      2. 注意到str_replace有双写绕过，但是数字限定了，需要使用字符串逃逸bro
  3. 顺带一提一个其他思路：注意到有文件包含，后面有文件写入，可不可以写入文件中进行包含执行？这里肯定不可以，主要还是看线索

源码

  1. www.zip的内容
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// dashboard.php
<p>你好，<?php echo htmlspecialchars($_SESSION['user']); ?>！</p>
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// index.php
<?php
session_start();
require 'user.php';
require 'class.php';

$sessionManager = new SessionManager();
$SessionRandom = new SessionRandom();

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $username = $_POST['username'];
    $password = $_POST['password'];

    $_SESSION['user'] = $username;

    if (!isset($_SESSION['session_key'])) {
        $_SESSION['session_key'] =$SessionRandom -> generateRandomString();
    }
    $_SESSION['password'] = $password;
    $result = $sessionManager->filterSensitiveFunctions();
    header('Location: dashboard.php');
    exit();
} else {
    require 'login.php';
}
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// class.php
<?php
class notouchitsclass {
    public $data;

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

    public function __destruct() {
        eval($this->data);
    }
}

class SessionRandom {

    public function generateRandomString() {
    $length = rand(1, 50);

    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $charactersLength = strlen($characters);
    $randomString = '';

    for ($i = 0; $i < $length; $i++) {
        $randomString .= $characters[rand(0, $charactersLength - 1)];
    }

    return $randomString;
    }


}

class SessionManager {
    private $sessionPath;
    private $sessionId;
    private $sensitiveFunctions = ['system', 'eval', 'exec', 'passthru', 'shell_exec', 'popen', 'proc_open'];

    public function __construct() {
        if (session_status() == PHP_SESSION_NONE) {
            throw new Exception("Session has not been started. Please start a session before using this class.");
        }
        $this->sessionPath = session_save_path();
        $this->sessionId = session_id();
    }

    private function getSessionFilePath() {
        return $this->sessionPath . "/sess_" . $this->sessionId;
    }

    public function filterSensitiveFunctions() {
        $sessionFile = $this->getSessionFilePath();

        if (file_exists($sessionFile)) {
            $sessionData = file_get_contents($sessionFile);

            foreach ($this->sensitiveFunctions as $function) {
                if (strpos($sessionData, $function) !== false) {
                    $sessionData = str_replace($function, '', $sessionData);
                }
            }
            file_put_contents($sessionFile, $sessionData);

            return "Sensitive functions have been filtered from the session file.";
        } else {
            return "Session file not found.";
        }
    }
}