Snappy is a PHP library allowing thumbnail, snapshot or PDF generation from a url or a html page. Prior to version 1.4.2, Snappy is vulnerable to PHAR deserialization due to a lack of checking on the protocol before passing it into the `file_exists()` function. If an attacker can upload files of any type to the server he can pass in the phar:// protocol to unserialize the uploaded file and instantiate arbitrary PHP objects. This can lead to remote code execution especially when snappy is used with frameworks with documented POP chains like Laravel/Symfony vulnerable developer code. If a user can control the output file from the `generateFromHtml()` function, it will invoke deserialization. This vulnerability is capable of remote code execution if Snappy is used with frameworks or developer code with vulnerable POP chains. It has been fixed in version 1.4.2.

Affected: Packagist: knplabs/knp-snappy

## Description

snappy is vulnerable to PHAR deserialization due to a lack of checking on the protocol before passing it into the `file_exists()` function. If an attacker can upload files of any type to the server he can pass in the phar:// protocol to unserialize the uploaded file and instantiate arbitrary PHP objects. This can lead to remote code execution especially when snappy is used with frameworks with documented POP chains like Laravel/Symfony vulnerable developer code. If user can control the output file from the `generateFromHtml()` function, it will invoke deserialization.

## Proof of Concept

Install Snappy via composer require `knplabs/knp-snappy`. After that, under snappy directory, create an `index.php` file with this vulnerable code.

```php <?php // index.php

// include autoloader require __DIR__ . '/vendor/autoload.php';

// reference the snappy namespace use Knp\Snappy\Pdf;

// vulnerable object class VulnerableClass { public $fileName; public $callback;

function __destruct() { call_user_func($this->callback, $this->fileName); } }

$snappy = new Pdf('/usr/local/bin/wkhtmltopdf'); // generate pdf from html content and save it at phar://poc.phar $snappy->generateFromHtml('<h1>Bill</h1><p>You owe me money, dude.</p>', 'phar://poc.phar'); ```

As an attacker, we going to generate the malicious phar using this script.

```php <?php // generate_phar.php

class VulnerableClass { } // Create a new instance of the Dummy class and modify i…

Affected: Ubuntu:Pro:16.04:LTS: civicrm, Ubuntu:Pro:18.04:LTS: civicrm, Ubuntu:Pro:20.04:LTS: civicrm, Ubuntu:Pro:22.04:LTS: civicrm

Snappy is a PHP library allowing thumbnail, snapshot or PDF generation from a url or a html page. Prior to version 1.4.2, Snappy is vulnerable to PHAR deserialization due to a lack of checking on the protocol before passing it into the `file_exists()` function. If an attacker can upload files of any type to the server he can pass in the phar:// protocol to unserialize the uploaded file and instantiate arbitrary PHP objects. This can lead to remote code execution especially when snappy is used with frameworks with documented POP chains like Laravel/Symfony vulnerable developer code. If a user can control the output file from the `generateFromHtml()` function, it will invoke deserialization. This vulnerability is capable of remote code execution if Snappy is used with frameworks or developer code with vulnerable POP chains. It has been fixed in version 1.4.2.