01 Jul

Reflected Cross-Site Scripting (XSS) Vulnerability in Newsletters

While looking into a vulnerability in a WordPress plugin closed on the Plugin Directory on Friday, so that we could warn the customers of our service about it, we noticed an indication that there might have been the same type of vulnerability in the plugin Newsletters as well and then found it had also been closed on the same day . A search over the plugin’s code and a bit of testing confirmed that it contains a reflected cross-site scripting (XSS). We don’t know if that led to the closure.

The plugin registers the function ajax_load_new_editor() to be accessible through WordPress’ AJAX functionality to those logged in to WordPress:

add_action('wp_ajax_newsletters_load_new_editor', array($this, 'ajax_load_new_editor'));

In four lines of code in that the value of the GET or POST input “contentarea” is output without being escaped, which permits reflected cross-site scripting (XSS). The first of those being:

<div class="postbox" id="contentareabox<?php echo $_REQUEST['contentarea']; ?>">

WordPress Causes Full Disclosure

Due to the moderators of the WordPress Support Forum’s continued inappropriate behavior we are full disclosing vulnerabilities in protest until WordPress gets that situation cleaned up, so we are releasing this post and then leaving a message about that for the developer through the WordPress Support Forum. You can notify the developer of this issue on the forum as well. Hopefully the moderators will finally see the light and clean up their act soon, so these full disclosures will no longer be needed (we hope they end soon). You would think they would have already done that, but considering that they believe that having plugins, which have millions installs, remain in the Plugin Directory despite them knowing they are vulnerable is “appropriate action”, something is very amiss with them (which is even more reason the moderation needs to be cleaned up).

Update: To clear up the confusion where developers claim we hadn’t tried to notify them through the Support Forum (while at the same time moderators are complaining about us doing just that), here is the message we left for this vulnerability:

Is It Fixed?

If you are reading this post down the road the best way to find out if this vulnerability or other WordPress plugin vulnerabilities in plugins you use have been fixed is to sign up for our service, since what we uniquely do when it comes to that type of data is to test to see if vulnerabilities have really been fixed. Relying on the developer’s information, can lead you astray, as we often find that they believe they have fixed vulnerabilities, but have failed to do that.

Proof of Concept

The following proof of concept will cause any available cookies to be shown in an alert box, when logged to WordPress. Major web browsers other than Firefox provide XSS filtering, so this proof of concept will not work in those web browsers.

Make sure to replace “[path to WordPress]” with the location of WordPress.

http://[path to WordPress]/wp-admin/admin-ajax.php?action=newsletters_load_new_editor&contentarea="><script>alert(document.cookie);</script>

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