Thursday, December 16, 2010
Wednesday, December 15, 2010
DDoS attacks are the rage this year, atleast in the latter part of the year. There have been numerous instances of successful DDoS attacks just in the past few months. Some of the current DoS/DDoS options seem to be LOIC, HTTP POST DoS and Jester's unreleased XerXes.
This post is about a DDoS technique I spoke about at BlackHat Abu Dhabi that uses two HTML5 features - WebWorkers and Cross Origin Requests. It is a very simple yet effective technique - start a WebWorker that would fire multiple Cross Origin Requests at the target. This is possible since Cross Origin Requests that use the GET method can be sent to any website, the restriction is only on reading the response which is anyway not of interest in this case. Sending a cross domain GET request is nothing new, you can even do that by embedding a remote URL in the IMG or the SCRIPT tag but the interesting part here is performance. My tests on Safari and Chrome showed that both the browsers were able to send more than 10,000 Cross Origin Requests in one minute.
Maybe its not that simple, there are few things to consider here. When you send the first request to a particular page and the response does not contain the 'Access-Control-Allow-Origin' header with a suitable value then the browser refuses to send more requests to the same URL. This however can be easily bypassed by making every request unique by adding a dummy query-string parameter with changing values. The number of requests/minute is also a variable. The browser sends a certain number of requests and when it receives the responses for those it sends in the next set of requests and so on. So as the server slows down the browser's requests/minute rating would also slow down. The figure 10,000 requests/minute was clocked against a server located in the internal network, against a target in the Internet it would realistically be between 3000-4000 requests/minute. If the attacker is planning to target an internal server by getting the employees of that company to visit this malicious URL then the 10,000 requests/minute rating would apply.
I am not going to release any PoC as this might probably be a bad time to do that but it shouldn't be very difficult to put together something for testing once you understand how it works. It should be relatively easy to block this attack at the WAF since all Cross Origin Requests contain the 'Origin' header, that way you can differentiate between legitimate and malicious requests.
Saturday, December 11, 2010
Tuesday, December 7, 2010
..if you love security, don't let the people at the top of the security industry dictate the terms by which you do your research, disclose your vulnerabilities, or do your job.You have a ton of potential, and life is too short.My Father used to tell me that if you love what you're doing you'll never work another day in your life.To paraphrase him - if you aren't having fun in security, you're doing something wrong.Put a smile on your face, and go do what makes you happy!
Monday, November 8, 2010
Tuesday, September 7, 2010
In this post I will show you a technique which will alow us to extend DSer and simplify the processing of modifying JAVA Objects. Before we start I would like to thank my colleague Chilik Tamir for introducing me to the XStream library and helping with this idea. XStream is a library to serialize JAVA objects to XML and back. Now getting back to the topic. Let's assume that we have a complex object that we encounter in our request or response packet as follows:
|Fig. 1: Demo app to generate complex JAVA objects|
|Fig. 2: Request showing raw serialized data captured in Burp|
|Fig. 3: XML generated from the JAVA serialized object|
|Fig. 4: XML after modification|
|Fig. 5: Edited request as shown in the Burp|
|Fig 6: Modified data processed by the application|
Tuesday, August 10, 2010
If you click on any URL you see the links don't actually change the page but loads them with ajax. http://touch.facebook.com/#profile.php actually loads http://touch.facebook.com/profile.php into a div on the page.
HTML 5 does not do much to solve browser security issues. In fact it actually broadens the scope of what can be exploited, and forces developers to fix code that was once thought safe.
var xhr = new XMLHttpRequest();xhr.cor = true;xhr.open("http://external.site/");
Tuesday, August 3, 2010
I ran the POC in Google Chrome and as each character was entered in to the Input box, there was a list of auto-complete suggestions that popped-up. The amount of information that was in those lists was scary. Jeremiah’s POC was not designed to capture the information in the auto-complete suggestion lists, it was only looking for values that got populated in to the textbox.
This is how it works:
- User is asked to place his mouse pointer in one section of the page. By following the mouse movement we know exactly where the pointer this is located.
- We create an input element of very small width (3px) and position it just a little above where the mouse pointer rests.
- Now using the same method used by Jeremiah a character is entered in to the input box.
- When the auto-complete suggestion list pops up, the first entry in the list is now right under the mouse pointer and is highlighted automatically.
- Now the Input box is moved a little upwards and step 3 is repeated and this time the mouse pointer is over the second entry in the suggestion list and it is highlighted.
As you can see the only interaction from the user is hitting the enter key periodically. Chrome allows a maximum of 6 auto-complete suggestions per character and if the user plays the game for a couple of minutes the entire auto-complete suggestion data can be stolen by the attacker.
The POC works best in Google Chrome running on Windows. Because in this set-up an Input element of 3px width has an auto-complete suggestion list also of 3px width, it only looks like a thin white strip. And with a cleverly selected background this 3px strip is camouflaged and becomes practically invisible as done in the POC.
In Google Chrome running on Linux (thanks to Mario for verifying this) the width of the auto-complete box is not affected by the width of the input element, so even if the input element is of 3px the pop-up list is of its normal width. It’s the same story with Firefox even on Windows. If the list is of its normal width then it cannot be hidden from the user, CSS overlay techniques don’t work, and the attack becomes very obvious for the victim to see.
Another factor that makes this attack possible is that when the pop-up list appears, the ‘mousemove’ event is triggered automatically and so the entry under the mouse pointer gets selected without the user having to move the mouse. I am not sure if this is a Google Chrome specific behavior or is common to all browsers, haven’t tested that yet.
The POC is available here and there is also a video if you would like to see the attack in action.
Monday, July 19, 2010
If you claim that "XSS is not a big deal" that means you never owned something by using it and that's your problem not XSS's
-Ferruh Mavituna, Author of XSS Shell, XSS Tunnel and NetSparker
Sunday, June 27, 2010
When a website is trying to create an Offline Application Cache, Firefox and Opera ask for user permission and only after the user permitting, the site is able to create this cache. With Google Chrome and Safari this step is skipped, any website can create an Application Cache without the user even knowing about it.
Now enter HTML5 Application Cache. Unlike a traditional cache, with Application Cache any file can be cached. For example, the root file ‘/’ of a site can be cached. Let’s say an application cache is created for ‘/’ of www.facebook.com. Then every time the user types in www.facebook.com in their browser this cached page would be fetched. If this was done with normal cache then when the user requests this page the browser would send a request to the server for this resource and only if the server responds with a 304 Not Modified response, would the cache be served. But for '/’ all sites would respond back with a 200 OK with the index page’s content and that is what would be loaded and not the cache
The point is that with Application Cache, root files can be cached, this cannot be done with a normal cache. An attacker could then create a malicious cache for the index page of every HTTP site as soon as the victim connects to an unsecured WiFi. For example for Facebook, if the index page is controlled by the attacker then he can capture the username and password of the victim. Facebook being a HTTP site (post authentication) can anyway be compromised by poisoning the normal cache. But Gmail?
Almost all users open Gmail by typing in gmail.com in the address bar and this means its http://gmail.com (remember SSLstrip??). The server responds to this with a redirect to http://mail.google.com/mail/. And when requested for http://mail.google.com/mail/ the server responds with https://www.google.com/accounts/ServiceLogin?service=mail&blahblah... There are two HTTP requests before the server redirects the user to an HTTPS page. Either of those can be cached using Application Cache, http://gmail.com/ or http://mail.google.com/mail/.
This is how the entire attack works:
Step1: The victim connects to an unsecured network controlled by the attacker.
Step2: The victim browses to any random website, even opening the browser would do as it would send a request for the home page.
Step3: The attacker responds to this request with a page which contains an hidden iframe pointing to http://mail.google.com/mail/ .
Step4: The victim’s browser sends a request for http://mail.google.com/mail/.
Step5: The attacker responds to this with his own copy of the Gmail login page that would look exactly like the actual login page but would include a backdoor to steal the victim’s credentials when entered. This page also includes the manifest attribute in the HTML element so that the page is cached.
Step6: Victim goes back to secured network (home/office) and types in gmail.com, gets redirected by Google server to http://mail.google.com/mail/
Step7: The browser would load the fake login page.
Step8: User enters his Gmail credentials in to it, the credentials are sent over to the attacker.
By poisoning or creating a malicious Application Cache, the victim’s credentials to all HTTPS-only websites can be stolen by an attacker.
I have made a POC for this attack using Imposter. The POC comes with a config file loaded with the payloads for Facebook and Gmail. The cached pages would load fake login pages from www.andlabs.org through an iframe. Once the victim enters his username and password these are stored locally in the victim’s browser in the LocalStorage of www.andlabs.org and the credentials are passed on to the parent frame using HTML5 PostMessage API. The parent frame logs the user in using these credentials. The entered credentials can be viewed by visiting, http://www.andlabs.org/hacks/viewcreds.html. The credentials are not sent to the AnD Labs server so it’s safe to try out the POC.
There is a video of the entire attack using the POC here. POC can be downloaded here.
One point of interest is the Manifest file. Everytime a cached file is requested for, the browser would request the server for the Manifest file and if the server responds with a 404 then the cache would be removed. Picking an existing file on the server as the Manifest file would solve this issue as the server would return a 200. This would not result in a update of the cache because the server would not include “text/cache-manifest” in the Content-Type header. Even without this the cache would be served the first time but would be removed after that, using this technique can keep the cached file alive till it is deleted by the user.
Coming back to Chrome and Safari, when I first realized that they were not prompting for user permission I thought it was a serious oversight. I even contacted both the security teams, however they didn’t consider this to be a security issue. But on closer look their stance made sense, it is because they treat Application Cache the same way as normal cache. When you delete cache in these browsers all Application Cache is also deleted. But in Firefox they are handled separately. Deleting normal cache does not delete Application Cache, it has to be deleted explicitly. It is difficult to say which approach is better but the idea of user permission prompt is more reassuring to me. Till then browsing in private/incognito mode should keep user’s safe.
Chris Evans pointed out on FD that root resources can been cached even by using the normal cache mechanism, so using Application Cache for that reason alone might not gives an edge to the attacker.
However, using Application Cache does have a major advantage over normal cache.
When a root resource is cached using normal cache, it is removed the moment the user hits refresh on that page, but Application Cache stays. This can give an attacker continued access to the victim's browser until the user explicitly clears the cache. In Firefox this has to be done explicitly for Offline Website data.
Sunday, June 13, 2010
With all these new possibilities we are going to have many new types of vulnerabilities and attacks. Security has been a prime consideration in the design of the HTML5 spec , for instance the design of the Web SQL Database API naturally encourages Prepared Statements and it is actually a little harder to introduce SQL Injection vulnerabilities. However implementation mistakes are going to be many and it would be interesting to study them. To help developers avoid more obvious mistakes when implementing these features I have written two detailed articles explaining what could go wrong and how it can be avoided. These articles are on the Web SQL Database and the Cross Origin Request features. Some of the points mentioned might look very obvious but I have personally in my experience doing Penetration tests seen much more obvious mistakes with very serious consequences.
The two articles are:
- Web SQL Database Security - http://code.google.com/p/html5security/wiki/WebSQLDatabaseSecurity
- Cross Origin Request Security - http://code.google.com/p/html5security/wiki/CrossOriginRequestSecurity
My original idea was to write about them in a series of blog posts but I was in luck because at around the same time Mario announced his HTML5 Security CheatSheet project. And when contacted he liked my idea and was nice enough to add me to his project. So now it is in the form of a Wiki page which is great because it can be updated constantly based on feedback/ideas from readers and findings of other researchers.
There is also a HTML5 Security Quick Reference Guide along with Live Demos of secure and insecure implementation of some features at http://www.andlabs.org/html5.html
All comments/suggestions/feedback are welcome.
Sunday, April 18, 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:
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
Tuesday, April 6, 2010
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.
var input_text = $(event.target).val();
//removed for clarity
$('#nomination_submit').html('Nominate <strong>' + input_text + '</strong>');
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.
Thursday, March 4, 2010
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.
Tuesday, March 2, 2010
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:
<input type="text" name="email" value=””></input>
<input type="hidden" name=”csrf-token” value="a0a0a0a0a0a"/>
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
//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
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.firstname.lastname@example.org HTTP/1.1
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.email@example.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.
<input type="text" name="email" value=""></input>
<input type="hidden" name="csrf-token" value="a0a0a0a0a0a">
//check if email is set
form.action = document.location; //document.location will give out the entire URL with parameters
form.method = "post";
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.
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.