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Analytics Stats Counter Statistics 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 Analytics Stats
Counter Statistics 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-20160803-0005

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Tested versions
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This issue was successfully tested on the Analytics Stats Counter
Statistics [2] WordPress Plugin version 1.2.2.5.

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Fix
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There is currently no fix available.

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Introduction
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The Analytics Stats Counter Statistics [2] WordPress Plugin analyses
visitors statistics on a WordPress site. A PHP Object injection [3]
vulnerability was found in the Analytics Stats Counter Statistics
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
wpadm_unpack() method. The input is taken directly from the POST request
as can be seen in the following code fragment:

wpadm.php:

if ( ! function_exists( 'wpadm_run' )) {
	function  wpadm_run($pl, $dir) {
		@set_time_limit(0);
		require_once dirname(__FILE__) . '/class-wpadm-method-class.php';
		$request_name = 'wpadm_'.$pl.'_request';
		if( isset( $_POST[$request_name] ) && ! empty ( $_POST[$request_name]
) ) {
			require_once dirname(__FILE__) . '/class-wpadm-core.php';
			$wpadm = new WPAdm_Core(wpadm_unpack($_POST[$request_name]), $pl,
$dir);
			echo '<wpadm>'.wpadm_pack($wpadm->getResult()->toArray()).'</wpadm>';
			exit;
		}
	}
}
	
	
if ( ! function_exists( 'wpadm_unpack' )) {
	/**
	 * @param str $str
	 * @return mixed
	 */
	function wpadm_unpack( $str ) {
		return unserialize( base64_decode( $str ) );
	}
}

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/analytics_stats_counter_statistics_wordpress_plugin_unauthenticated_php_object_injection_vulnerability.html
[2] https://wordpress.org/plugins/stats-counter/
[3] https://www.owasp.org/index.php/PHP_Object_Injection