As written in: http://security.pass.pl/adv/160406_XSS_tlen_pl.txt 

::File: 060416_XSS_tlen_pl
::Date: 16 Feb 2006
::Author: Tomasz Koperski  
::URL: http://security.pass.pl 



::1::Overview::
Tlen.PL e-mail system is affected to cross-site scripting vulnerability, not validating HTML tags in e-mail message subject. 



::2::Description::
Tlen.PL is a popular Polish IM system provided by o2.pl, which includes e-mail accounts, and e-mail client built into the 
communicator software (under Windows it is actualy an instance of Internet Explorer, displaying webmail system). 
Depending on the server 'assigned' to the account (varying probably by the date of registration), webmail client does 
not validate e-mail subject for HTML tags, allowing attacker to inject script code.
The vulnerable server is accessed by default with Tlen.pl IM client (by older accounts).
The vulnerable server does not provide webmail services through default web browser access
(using for ex.: http://poczta.o2.pl, http://mail.tlen.pl), yet it is still accessible under http://beta.mini.tlen.pl 
and used inside Tlen.pl IM client.
On the account tested (login: koper, served by beta.mini.tlen.pl, 193.17.41.32, registered over 5 years ago), the lenght of 
subject displayed is 28 characters, which is the lenght an attacker can use to inject HTML.



::3::Impact::
An attacker could include some of this code inside the subject field of e-mail sent to the target account: