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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 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


Corrections,if any, is always appreciated!


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.


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