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YITH WooCommerce Compare 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 YITH WooCommerce
Compare 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-20160803-0006

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Tested versions
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This issue was successfully tested on the YITH WooCommerce Compare [2]
WordPress Plugin version 2.0.9.

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Fix
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This issue is resolved in YITH WooCommerce Compare [3] version 2.1.0.

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Introduction
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The YITH WooCommerce Compare [2] WordPress Plugin is an extension of
WooCommerce plugin that allow your users to compare some products of
your shop. A PHP Object injection [4] vulnerability was found in the
YITH WooCommerce Compare 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
__construct() method. The input is taken directly from the
yith_woocompare_list cookie as can be seen in the following code
fragment:

includes/class.yith-woocompare-frontend.php:

/**
	 * Constructor
	 *
	 * @return YITH_Woocompare_Frontend
	 * @since 1.0.0
	 */
	public function __construct() {
	
		// set coookiename
		if ( is_multisite() ) $this->cookie_name .= '_' .
get_current_blog_id();
	
		// populate the list of products
		$this->products_list = isset( $_COOKIE[ $this->cookie_name ] ) ?
json_decode( maybe_unserialize( $_COOKIE[ $this->cookie_name ] ) ) :
array();

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/yith_woocommerce_compare_wordpress_plugin_unauthenticated_php_object_injection_vulnerability.html
[2] https://wordpress.org/plugins/yith-woocommerce-compare/
[3]
https://downloads.wordpress.org/plugin/yith-woocommerce-compare.2.1.0.zip
[4] https://www.owasp.org/index.php/PHP_Object_Injection