Thursday, December 22, 2011

Cross Origin Resource Jacking (CORJacking) - DOM based attack vector

CSRF and UI Redressing (Click/Tab/Event Jacking) attack vectors are popular ways to abuse cross domain HTTP calls and events. HTML5, Web 2.0 and RIA (Flash/Silverlight) applications are loaded in browser with native state or using plug-ins. DOM used to be an integral part of the browser and now it is becoming even more important aspect with reference to web applications. Web applications are using DOM in very complex and effective way to serve their client better and leveraging all possible features allowed by DOM specifications.

There are many applications run as single DOM app and once it gets loaded, it remains in scope across the application life cycle. CORS and SOP have to play critical role in protecting Cross Origin Resources and control relevant HTTP calls. HTML5 and RIA applications are having various different resources like Flash files, Silverligh, video, audio etc. These resources are loaded in their own little object space which is defined by specific tag. These resources are accessible by DOM and can be manipulated as well. If DOM is forced to change underlying resource on the fly and replaced by cross origin/domain resource then it causes Cross Origin Resource Jacking (CROJacking).

Let’s assume there are two domains – and Foobank application is having flash driven application and it has its own login swf (login.swf) file. This flash component is loaded via object in the browser. If by DOM call this login.swf file is replaced by similar file residing on then it will cause CORJacking and user would be under impression that he/she is using resources. Also, reverse would be possible as well. loads resources residing on domain and it will cause reverse CORJacking.

Here is a small DEMO of CORJacking with Flash resource.

Here is the object tag loading flash component

HTML page is loaded in the browser and this object which is coming from domain is being loaded. Assuming this page has DOM based issue and possible to inject/manipulate this value. Hence, if we want to access src of this object tag then through DOM we get its access.

Interestingly document.getElementsByName(‘Login’).item(0).src is not just read only value, one can assign a cross origin resource to it on the fly.

Hence, below line will actually change the resource and loads login.swf file from domain.

document.getElementsByName(‘Login’).item(0).src = ‘’

This will clearly hijack the resource and user will be under impression that it is negotiating with foobank’s login component but actual component is from evil domain. This is the case of CORJacking and reverse can be done as well. Evil domain can load Foobank component and causes reverse CORJacking.

Since browser is allowing these Cross Origin Resource access one needs to embed defense in similar way we are doing for ClickJacking. Before component being loaded, component should have sense of domain and disallow its execution on cross domain as far as reverse CORJacking is concern. For CORJacking one needs to lock object using JavaScript, controlling stream and avoid DOM based injection issues to stop CORJacking exploitation.

[Note – This type of loading is not restricted to one type of resource only, it is applicable to different types of resources and browser's ability to process cross origin resource loading. It is possible to create various different variants of these attack vector like flashjacking, silverlightjacking, mediajacking etc. inherited from UI redressing family - interesting area for research, will add a paper on it soon.]

Thursday, December 08, 2011

Top 10 HTML5 Threats & Attack Vectors

Emerging as popular standard to create Rich Internet Applications and competing with technology stacks like Adobe’s Flex/Flash and Microsoft’s Silverlight is  HTML5[1]. HTML5 brings several new features and functionalities that allow developers to create really attractive and robust applications.  These applications can run on any browser and platform, although with some limitations. HTML5 applications are also supported by mobile devices. Hence, you can create your application once and run it on several devices and browsers. Each time, every new technology stack throws up new security challenges and vulnerabilities. HTML 5, though very promising, is no different. There are security concerns that need to be addressed when creating applications. Let us look at the top 10 possible attack vectors associated with HTML5 and modern browser architecture.

Read full article here (

Top 10 Attack Vectors

1.  ClickJacking & Phishing by mixing layers and iframe         
2.  CSRF and leveraging CORS to bypass SOP             
3.  Attacking WebSQL and client side SQL injection
4.  Stealing information from Storage and Global variables 
5.  HTML 5 tag abuse and XSS          
6.  HTML 5/DOM based XSS and redirects  
7.  DOM injections and Hijacking with HTML 5          
8.  Abusing thick client features      
9.  Using WebSockets for stealth attacks    
10.Abusing WebWorker functionality           

Browser Attack Surface and Layers

Friday, December 02, 2011

Double eval() for DOM based XSS

DOM based XSS are becoming relatively common with Web 2.0 and Ajax driven applications. DOM based applications are using eval() method to inject new stream into the existing DOM. In certain cases it is becoming tricky to pass on the values for pen-testing and to create an abuse/exploit scenario. Recently during consulting we came across different DOM based XSS and objective is to get a pop-up to confirm the vulnerability. If we get an eval call then it is possible to double eval-ing to convert text back into payload.

Here is a simple scenario; it can be complicated on case to case basis.
For example, we have following line in the code

eval('getProduct('+ koko.toString()+')');

Here “koko” is coming from URL or controlled by user. Hence, if we pass on the value in following URL it gets to the “getProduct” function.

Testing scenario is simple, it causes DOM based XSS with following condition.

We are passing payload terminating function, ending statement and commenting out rest of the script. We get a simple pop-up if we pass on following code.

But to prove a point if we want to craft any other payload where we need to send single quote, for example want to execute “document.getElementsByName('Login')” will not work since we have that single quote that will raise syntax error. For simplicity if we pass on alert(‘hi’), it will not work and we will not get popup in above scenario.

We get following error in the browser.

Error: syntax error
Source File:;elval(alert(%27hi%27));//
Line: 37, Column: 29
Source Code:

Interestingly, we can leverage double eval() in this case, we pass on following payload and let’s see what happens…

It will avoid error and we will get a pop-up. What we did was simple, we used fromCharCode function and passed on decimal values for alert(‘hi’) here, first eval will convert it into string and second eval will execute the code. Hence, double eval can rescue while testing DOM based XSS.

Curiously I searched this trick on web if people are using it and came across this article -
Double eval() can be leveraged for string operations and concatenation.

Monday, November 28, 2011

CSRF with JSON – leveraging XHR and CORS

Same Origin Policy (SOP) dictates cross domain calls and allows establishment of cross domain connections. SOP bypasses allow CSRF attack vector, an attacker can inject a payload on cross domain page that initiate a request without consent or knowledge of the target user. HTML 5 is having one more policy in place called CORS (Cross Origin Resource Sharing). CORS is a “response blind” technique and controlled by extra added HTTP header “orgin” and their variants but it allows request to hit the target in one way direction. Hence, it is possible to do one-way CSRF. It is possible to initiate CSRF vector using XHR-Level 2 on HTML 5 pages and can prove really lethal attack vector. XHR establishes a stealth connection and remains much hidden, XHR connection can be set using “withCredentials” as true along with POST method. It allows cookie to replay and helps in crafting successful CSRF scenario or session riding. Interestingly HTML 5 along with CORS allows performing file upload CSRF as well. It is possible to craft a JavaScript using XHR and inject JSON payload as cross domain. If server side code on JSON library is not validating the “Content-Type” then it will process the request and allows successful CSRF.
For example,

Here is a script which will do CSRF on cross domain.

Here, we have “Content-Type” as “text-plain” and no new extra header added so CORS will not initiate OPTIONS to check rules on the server side and directly make POST request. At  the same time we have kept credential to “true” so cookie will replay.

On the wire we can see following request.

As you can see cookie is replayed and JSON POST has been initiated. We get following response back from application.

Application processed the request and sent JSON back. It is clear case of CSRF. This can be applied to other streams as well.

Wednesday, March 30, 2011

Training at Syscan - Web Hacking – Threats & Countermeasure

Web Hacking – Threats & Countermeasure
Introduction and adaptation of new technologies like Ajax, Rich Internet Applications and Web Services has changed the dimension of Web Hacking and Security. We are witnessing new ways of hacking and exploiting web based applications and it needs better understanding of technologies to perform penetration testing and assessment of web security. The course is designed by the author of “Web Hacking: Attacks and Defense”, “Hacking Web Services” and “Web 2.0 Security – Defending Ajax, RIA and SOA” bringing his experience in application security and research as part of curriculum to address new challenges for pen-testers, consultants, auditors and QA teams. Web Hacking 2.0 is extensively hands-on class with real life challenges and lab exercises. Participants would be methodically exposed to various different attack vectors and exploits. The learning sessions feature real life cases, hands one exercises, new scanning tools and exploits.

Visit syscan training page - here

Wednesday, March 23, 2011

HTML 5, XHR (L2) and DOM (L3) - Top 10 Attacks

Current stack and technology surface

Top 10 Attack Vectors

1. XSS abuse with tags and attributes
2. DOM based XSS and Redirects
3. Stealing from the storage
4. Injecting and Exploiting WebSQL
5. Abusing network API and Sockets
6. CSRF across streams – JSON, AMF and XML
7. Sandbox attacks and ClickJacking
8. Abusing new features like drag-and-drop
9. Botnet/Spynet gets persistent life using WebWorkers
10. Threats to widgets and mashups