Skip to main content

How cookie can leak

Today I was having a chat with my friend Vaibhav about few vulnerabilities in one of the applications. In order of that he asked me it's really necessary to mark cookie as "Secure". Well, depends...if your whole application is on https then you should always go for "Secure" attribute. Cookies set with the "Secure" keyword will only be sent by the browser when connecting by a secure means (HTTPS). Apart from that there is no distinction - if "Secure" is absent, the cookie may be sent over an insecure connection.

We have seen a lot of cases where the cookie is leaked and sent over from https to http:

1. If your page contains mixed contents, ie. if you are including some links that is on http then the cookie may be leaked. For example, if your application uses url https://example.com and you are including someother links in the page using http://, the browser may warn you as "this page contains both secure and nonsecure items".

2. If you are visiting page with https:// link but you click on a third party link which is on http:// that may leak the cookies.

3. The browser may cache the cookies if not marked as secure.

So mainly there are 4 conditions:

* HTTP Cookie, with "Secure" will be returned only on HTTPS connections
* HTTPS Cookie, with "Secure" will be returned only on HTTPS connections
* HTTP Cookie, without "Secure" will be returned on HTTP or HTTPS connections
* HTTPS Cookie, without "Secure" will be returned on HTTP or HTTPS connections (could leak secure information)

So, HTTP Cookies can be read by HTTP or HTTPS. HTTPS Cookies can only be read by HTTPS, that is if you set Secure = True on the cookie.
Also how and when to setup "Secure" flag, you can visit my last posts-this and this

References:
http://www.w3.org/Protocols/rfc2109/rfc2109
http://stackoverflow.com/questions/2163828/can-cookies-set-using-http-be-read-using-https

Corrections,if any, is always appreciated!

Comments

Vaibhav said…
Hi Nilesh,

I had a discussion with the client and we came to the discussion that the application only has HTTPS port open i.e 443 and each and every request of the application goes through HTTPS as no HTTP port 80 is being used. Is it still necessary to secure the cookies.

So your point helped me to answer the question that "Non Secure cookies can be cached in the memory" :) and that helped me to push client to implement Secure TAG to all the cookie value.

Thanks
Vaibhav

Popular posts from this blog

Ardilla- New tool for finding SQL Injection and XSS

Three Researchers -- MIT's Adam Kiezun , Stanford's Philip Guo , and Syracuse University's Karthick Jayaraman -- has developed a new tool ' Ardilla ' that automatically finds and exploits SQL injection and cross-site scripting vulnerabilities in Web applications. It creates inputs that pinpoint bugs in Web applications and then generates SQL injection and XSS attacks. But for now Ardilla is for PHP -based Web app only. The researchers say Ardilla found 68 never-before found vulnerabilities in five different PHP applications using the tool -- 23 SQL injection and 45 XSS flaws. More information is awaited. For their attack generation techniques refer to their document at: http://www.cs.washington.edu/homes/mernst/pubs/create-attacks-tr054.pdf

Combining power of Fiddler with Burp

Both are pretty powerful tools when it comes to intercept and modify http communications. But at some point of time, they become even more powerful combo if tied with each other. They complement each other. In a recent pentest I came across a similar situation where in Burp was not able to intercept a specific kind of traffic and Fiddler came to rescue. The application was designed to upload video. The initial communication was straight forward, I mean logging into application, filling up the video details etc. And all these were easily captured by Burp except the point where you hit the Upload Video and it connects to a different server and surprisingly it was not captured by Burp, not sure why, even after repeated attempts. So, I fired Fiddler to see if the it sees this request. But it's a;ways to play with requests using Burp due to it's various functionalities like, Intruder, Repeaters etc. But it was necessary to capture this request in Burp. So the below steps can be

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