Classic Cross Site Scripting: Gibson Research Corporation

["http-equiv () excite com" <http-equiv () malware com>]

Wednesday, May 01, 2002

The following represents a classic [fitting] working example of the 
dangers of Cross Site Scripting.  

[see: http://www.cert.org/advisories/CA-2000-02.html 
http://www.cert.org/archive/pdf/cross_site_scripting.pdf]

Gibson Research Corporation http://www.grc.com is an interesting site 
covering a wide variety of security topics for newcomers. Cursory 
research suggests that it enjoys a substantial loyal following who 
trust it implicitly.

The problem is two-fold:

1. The site has a web based discussion forum
2. The site has a custom 'filter', the so-called: "Gibson Research 
Corporation's IIS Advanced Prophylactic Filter"

This custom 'filter' is supposed to protect the server 
from 'malicious abuse' and both 'detect and block' invalid requests 
submitted to the server:

http://www.grc.com/apf/

[screen shot: http://www.malware.com/flitty.png 25KB]

Unfortunately, what it actually does is allow us to inject our own 
html code through grc.com's secured server.  This is particularly 
ticklish as it does not take much to conjure up a scenario where we 
construct a 'fake' e-commerce page, say peddling a book or 'gadget' 
download and simply invite the loyal following to go and submit their 
credit card details to our custom form.

The site grc.com well known and trusted. The page is on a secured 
server with valid certificates.

Ripe For Picking™

Crude Working example:

note: custom crafted for Internet Explorer 5.5 and 6

http://www.malware.com/grc.html

[screen shot: http://www.malware.com/lucre.png 11KB]

Notes:

1. Watch where you "point and click". It's all smoke and mirrors out 
there.
2. 3 mail messages within 72 hours to support @ grc.com remain 
unanswered to date.


End Call

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