I was trying to look at this from the standpoint of how does the 
offending script get on your site in the first place.  Let's say you 
have a discussion board and you want to make sure no one puts nasty suff 
in SCRIPT tags in their postings.  But from what I gather is your 
interested in blocking on the way out.  I'll re-read the CERT advisory.

gio

Jon Stevens wrote:

>on 11/20/01 10:58 AM, "Steve Giovannetti" <[EMAIL PROTECTED]> wrote:
>
>>In the interest of  breaking the chains of my cross site scripting
>>ignorance, I'm assuming that the offending SCRIPT needs to be blocked
>>from POST or GET requests made by users to JSP/Servlets on the target
>>server?
>>
>
>Nope. The only thing that needs to be done is that certain content needs to
>be filtered when it is sent to the browser client so that it is not
>interpreted by the client in a bad way.
>
>> Wouldn't an input filter on the servlet just do the trick?
>>
>
>Filtering all of the content would be a performance killer and doesn't make
>much sense. You also don't want to filter input, only output.
>
>I'm not trying to solve the problem of doing the filtering of the content
>that I want to filter...I know how to do that...I'm trying to solve the
>problem that no one has created any code in Java (that I can find) to deal
>with the CSS issue itself.
>
>Part of the problem with this security hole is that, for some reason, it is
>hard for a lot of people to even get a basic comprehension of it (even
>though it is so well documented). I think that is why a lot of people just
>ignore it as being a problem.
>
>-jon
>
>
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