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InfiniteWP Client WordPress Plugin unauthenticated PHP Object injection
vulnerability
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Yorick Koster, June 2016

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Abstract
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A PHP Object injection vulnerability was found in the InfiniteWP Client
WordPress Plugin, which can be used by an unauthenticated user to
instantiate arbitrary PHP Objects. Using this vulnerability it is
possible to execute arbitrary PHP code.

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OVE ID
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OVE-20160803-0004

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Tested versions
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This issue was successfully tested on the InfiniteWP Client [2]
WordPress Plugin version 1.5.1.3/1.6.0.

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Fix
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Input validation was added to version 1.6.1.1 of InfiniteWP Client to
mitigate this issue. JSON support was added to InfiniteWP Client version
1.6.3.2 [3], which will eventually replace the serialized data.

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Introduction
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The InfiniteWP Client [2] WordPress Plugin allows users to manage
unlimited number of WordPress sites from their own server. A PHP Object
injection [4] vulnerability was found in the InfiniteWP Client WordPress
Plugin, which can be used by an unauthenticated user to instantiate
arbitrary PHP Objects.

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Details
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This issue is possible due to an unsafe call to unserialize() in the
iwp_mmb_parse_request() method. The input is taken directly from the
POST body as can be seen in the following code fragment:

init.php:

if( !function_exists ('iwp_mmb_parse_request')) {
	function iwp_mmb_parse_request()
	{
		global $HTTP_RAW_POST_DATA;
		$HTTP_RAW_POST_DATA_LOCAL = NULL;
		$HTTP_RAW_POST_DATA_LOCAL = file_get_contents('php://input');
		if(empty($HTTP_RAW_POST_DATA_LOCAL)){
			if (isset($HTTP_RAW_POST_DATA)) {
				$HTTP_RAW_POST_DATA_LOCAL = $HTTP_RAW_POST_DATA;
			}
		}
	
		ob_start();
	
		global $current_user, $iwp_mmb_core, $new_actions, $wp_db_version,
$wpmu_version, $_wp_using_ext_object_cache;
		$data = base64_decode($HTTP_RAW_POST_DATA_LOCAL);
		if ($data){
			//$num = @extract(unserialize($data));
			$unserialized_data = @unserialize($data);
			if(isset($unserialized_data['params'])){ 
			$unserialized_data['params'] =
iwp_mmb_filter_params($unserialized_data['params']);
		}

It has been confirmed that this issues can be used to execute arbitrary
PHP code.
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References
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[1]
https://sumofpwn.nl/advisory/2016/infinitewp_client_wordpress_plugin_unauthenticated_php_object_injection_vulnerability.html
[2] https://wordpress.org/plugins/iwp-client/
[3] https://downloads.wordpress.org/plugin/iwp-client.zip
[4] https://www.owasp.org/index.php/PHP_Object_Injection