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Javascript DDoS Tool Analysis

Published: 2012-01-22
Last Updated: 2012-01-23 18:16:34 UTC
by Johannes Ullrich (Version: 1)
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  Last week's denial of service attack agains the Department of Justice (, the FBI ( and other sites didn't just rely on Anonymous's favorite tool Low Orbit Ion Canon. Instead, a new method was employed to recruit denial of service clients.

  The new method uses some pretty simple javascript to launch the attack. The folowers are usually requested to visit a particular web page. The page includes a simple form to adjust the denial of service attack parameters but just launches the attack with default parameters as the page is opened in the browser.

  IMPORTANT: The script will start running as soon as the user vists the page. You do not have to press the "fire" button.

  Javascript code retrieving the parameters:

var fireInterval;
var isFiring = false;
var currentTime = new Date()
var lastSuccess = currentTime.getTime();
var requestedCtrNode = document.getElementById("requestedCtr"),
succeededCtrNode = document.getElementById("succeededCtr"),
failedCtrNode = document.getElementById("failedCtr"),
targetURLNode = document.getElementById("targetURL")

   an unused part of the code hints at plans to implement a hash table, likely to exploit the recently discussed hashtable denial of service vulnerability

var requestsHT = {}; // requests hash table, may come in handy later

  Originally, I figured the attack may take advantage of XMLHTTPRequest. Instead, the code takes a simpler route. It just changes an image URL to a URL on the attacked page. I suspect that this method is more reliable as it does not require the client to implement XMLHTTPrequest Level 2 or XDomainrequest but should work with pretty much any client.

It will not necessarily retrieve an actual image, but just whatever URL was targeted, followed by an "id" parameter and a "msg" (which is also set by the user). This format should make it pretty easy to filter the attacks at a web application firewall. Even other content sensitive firewalls should be able to deal with this.

Sample weblog:

GET /?id=1327271393334&msg=No%20A%20la%20CENSURA%20EN%20INTERNET%A1%A1%A1 
 HTTP/1.1" 200 8395 

  In order to prevent crashing the browser, the script will limit the number of outstanding requests. The script attempts to send 5,000 requests per second. I tested it directing my requests to a lab web server across a pretty slow VPN connection. It managed to create about 5 requests per second. The referer for the request will be the URL of the attack page. The user's user agent is not altered. 

 Update: Spiderlabs did a nice analysis of this tool, including other "LOIC" variants just about a year ago:

Johannes B. Ullrich, Ph.D.
SANS Technology Institute

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