RE: Cross Site Scripting Vulnerabilities - XSS
From: Matt Andreko (mandrekoat_private)
Date: Tue Aug 06 2002 - 14:56:04 PDT
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I am kinda new to XSS, but am intrigued by how it works. I have found
sometimes you can get javascript messages to pop up and such, but if
it's not being stored in a database, what good is it?
Take for example Iwillusa.com (a motherboard maker's website). They
have a product page that I saw had some html in the URL:
http://www.iwillusa.com/products/spec.asp?ModelName=DVD266>u</i>-RN&Su
pportID=
I edited it and it became:
http://www.iwillusa.com/products/spec.asp?ModelName=DVD266u-RN
language=javascript>alert(document.cookie);</script>&SupportID=
I'm fully able to get a javascript error. However, what good does this
do, if it's not stored anywhere?
-----Original Message-----
From: Bill Pennington [mailto:billpat_private]
Sent: Tuesday, August 06, 2002 10:29 AM
To: Jason binger; pen-test; webappsec
Subject: Re: Cross Site Scripting Vulnerabilities - XSS
Cross posting to webappsec because I know other people will have
comments
and suggestions.
I have done more XSS testing that I care to remember.
There are no tool that I am aware of that can accurately test for XSS
issues
in a web application. Some scanners have pretty good test for web server
and
application server XSS issues (like request
<SCRIPT>alert("foo")</SCRIPT>.jsp and exploit the 404 handler), Nessus
and
nikto come to mind.
For XSS testing I use a browser and a cheat sheet, a list of XSS strings
to
inject. My testing goes something like this:
Assuming I am looking at a URL based variable, VAR=
1. Determine if the variable is displayed on the screen. Change
VAR=realcontent to VAR=foo. This should generate an error message but it
might not. On the resulting page, view source and search for foo. Note,
you
might want to pick a less common string to make searching easier.
If foo is not on the resulting page you can not perform a URL based XSS
attack. The data might be stored and displayed latter though. Keep an
eye
out for it :-)
2. See how the application handles "<" and ">". Now change the variable
to
VAR=<foo>. Again view source on the returned page and look for <foo>. If
<foo> is present you most likely have an XSS issue. If you see something
like %ltfoo> then the variable is not vulnerable.
3, Now you just need to build an actual bit of client code and see if it
gets gets executed. Change VAR= to VAR=<SCRIPT>alert("XSS");</SCRIPT>
When
you submit the page you should get a pop-up box that says XSS on your
screen. If you do not get the pop-up, view source and find your string
and
make sure the proper syntax is in place. Some variables to put in
strange
places and you may need to format your injection string differently. If
you
are getting the full string returned to the browser without modification
it
is vulnerable, you just need to figure out the proper format. Most
likely
you need to close out another tag or a set of quotes before you XSS code
is
inserted.
The above steps are a bit redundant but they are part of testing the
application for all known issues, not just XSS. You could just do step 3
but
you might miss a bit of important info along the way. Most automated
tools
will only catch the simple XSS attacks, the more difficult ones are
passed
over.
Hope that helps!
On 8/3/02 10:52 PM, "Jason binger" <cisspstudyat_private> wrote:
> Has anyone on the list done much with testing for XSS
> vulnerabilities?
>
> Has anyone written a simple work program to test for
> these vulnerabilities that they are happy to
> distribute so others can do basic testing for these
> vulnerabilities?
>
> There a few papers out on this topic, but none that I
> hve seen that really focus on the testing side of
> things.
>
> Thanks
>
> __________________________________________________
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: Wed Aug 07 2002 - 12:13:40 PDT