WordPress and Drupal websites Vulnerable to DoS attack which can make them completely inaccessible

Pierluigi Paganini August 07, 2014

The popular expert Nir Goldshlager has discovered an XMLRPC vulnerability which affects millions WordPress and Drupal websites exposing them to DoS Attack.

If your website is based a WordPress or Drupal CMS you need to urgently update it to the last version released due to the presence of a critical vulnerability in the implementation of XMLRPC. XMLRPC is a remote procedure call (RPC) protocol which uses XML to encode its request and the HTTP as a carrier. The vulnerability is critical because millions of websites currently use WordPress and Drupal, the XML vulnerability is present in WordPress versions from 3.5 to 3.9.1 and Drupal versions from 6.x to 7.x.
The critical flaw, which affects all previous versions of WordPress, could be exploited by an attacker to conduct a Denial of Service (DoS) attack against our our website.
The vulnerability in the CMSs was discovered by the popular expert Nir Goldshlager, it is a problem related to the PHP’s XML processor that was promptly fixed by Michael Adams and Andrew Nacin of the WordPress security team and David Rothstein of the Drupal security team.
As explained by the research Goldshlager in his blog post, a hacker could exploit a know technique of attack, the XML Quadratic Blowup Attack, to make the targeted website completely inaccessible instantly due to the saturation of memory, CPU and of the pool of open connections.

Goldshlager highlights the similitude of the XML quadratic blowup attack with the Billion Laughs attack, it basically exploits the use of entity expansion, this means that it replicates one large entity using a couple thousand characters repeatedly.

“A medium-sized XML document of approximately two hundred kilobytes may require anywhere within the range of one hundred MB to several GB of memory. When the attack is combined with a particular level of nested expansion, an attacker is then able to achieve a higher ratio of success.”

In the following example provided by the expert, if the attacker defines the entity “&x;” as 55,000 characters long, and uses this entity 55,000 times inside the XML “DoS” element, the parser will expand to 2.5 GB the document causing the saturation of resources of targeted website.

<?xml version=”1.0″?> 
<!DOCTYPE DoS [!<ENTITY a "xxxxxxxxxxxxxxxxx...">]>

wordpress Drupal hacking

Following a video Proof of Concept of the attack on WordPress published by Goldshlager, while the PoC Exploit: (128MB Memory limit) is available at the address below


Both WordPress and Drupal have released an update today to fix the problem, all users that have chosen to manually update their CMS instance, urge to upgrade it to the latest version.

Pierluigi Paganini

(Security Affairs –  Drupal, WordPress, hacking)  

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