On 1/7/2013 8:43 AM, Flying-w wrote:
> I have a GWT application that among many things shows PDFs that are
> stored on the server side. I have a security related question, as
> described below.
>
> When a user logs in through a dialogue on the client side, I make a
> note of the userid they entered while processing the login on the
> server side. This is all done through the normal GWT RPC Infrastructure:
>
> HttpSession session = getThreadLocalRequest().getSession();
> session.setAttribute("USER", userId);
>
> I have a separate servlet that is responsible for locating and
> delivering PDF content back to the browser when requested. When the
> user clicks a button in the GWT client, I open a new browser window
> and address the servlet to produce the desired PDF. A reference to
> the name of the PDF required is stored in a client side cookie (and
> transmitted in the HTTP request).
>
> Window.open(GWT.getModuleBaseURL() + "Showpdf", "PDF Viewer", "");
>
> The servlet needs to check whomever is making the request is
> authorised to view the PDF requested, and checks the user name stored
> in the HttpSession earlier:
>
> HttpSession session = request.getSession();
> String user = (String)session.getAttribute("USER");
> // Do whatever is required to check the user can access the required PDF
>
> Is this approach is safe from hacking?
Probably not. Rule #1: The client computer is an environment not under
your control. It can be hacked. It might /not/ be hacked, but that
doesn't mean it /can't/ be hacked. The same goes for whatever Javascript
is running on the client. Don't assume that any Javascript comes from a
web browser environment, or that it even comes from a PC.
> Is there a way the user name can be spoofed by a hacker to gain
> access to a PDF they are not authorised for? Is there another way of
> doing this?
This is a variant of a common technique for delivering low-value digital
content.
The tradeoff is the value of the PDF vs. the strength of the safe in
which the PDF is contained. If the PDF is {low value|cheap} and the safe
is expensive, that's not a good tradeoff. If the PDF is
{expensive|valuable} than you might want to think of other delivery methods.
Cheers,
jec
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