Rooting a Logitech Harmony Hub: Improving Security in Today's IoT World


FireEye’s Mandiant Red Team recently discovered vulnerabilities
present on the Logitech Harmony Hub Internet of Things (IoT) device
that could potentially be exploited, resulting in root access to the
device via SSH. The Harmony Hub is a home control system designed to
connect to and control a variety of devices in the user’s home.
Exploitation of these vulnerabilities from the local network could
allow an attacker to control the devices linked to the Hub as well as
use the Hub as an execution space to attack other devices on the local
network. As the Harmony Hub device list includes support for devices
such as smart locks, smart thermostats as well as other smart home
devices, these vulnerabilities present a very high risk to the users.

FireEye disclosed these vulnerabilities to Logitech in January 2018.
Logitech was receptive and has coordinated with FireEye to release
this blog post in conjunction with a firmware update (4.15.96) to
address these findings.

The Red Team discovered the following vulnerabilities:

  • Improper certificate
  • Insecure update process
  • Developer
    debugging symbols left in the production firmware image
  • Blank root user password

The Red Team used a combination of the vulnerabilities to gain
administrative access to the Harmony Hub. This blog post outlines the
discovery and analysis process, and demonstrates the necessity of
rigorous security testing of consumer devices – particularly as the
public places an increasing amount of trust in devices that are not
just connected to home networks, but also give access to many details
about the daily lives of their users.

Device Analysis

Device Preparation

Publicly available
indicated the presence of a universal asynchronous
receiver/transmitter (UART) interface on some of the test points on
the Harmony Hub. We soldered jumper wires to the test pads, which
allowed us to connect to the Harmony Hub using a TTL to USB serial
cable. Initial analysis of the boot process showed that the Harmony
Hub booted via U-Boot 1.1.4 and ran a Linux kernel (Figure 1).

Figure 1: Initial boot log output from
UART interface

After this point in the boot process, the console stopped returning
output because the kernel was not configured with any console
interfaces. We reconfigured the kernel boot parameters in U-Boot to
inspect the full boot process, but no useful information was
recovered. Furthermore, because the UART interface was configured to
only transmit, no further interaction could be performed with the
Harmony Hub on this interface. Therefore, we shifted our focus to
gaining a better understanding of the Linux operating system and
associated software running on the Harmony Hub.

Firmware Recovery and Extraction

The Harmony Hub is designed to pair with a companion Android or iOS
application over Bluetooth for its initial configuration. We created a
wireless network with hostapd and installed a Burp Suite Pro CA
certificate on a test Android device to intercept traffic sent by the
Harmony mobile application to the Internet and to the Harmony Hub.
Once initial pairing is complete, the Harmony application searches for
Harmony Hubs on the local network and communicates with the Harmony
Hub over an HTTP-based API.

Once connected, the Harmony application sends two different requests
to Harmony Hub’s API, which cause the Harmony Hub to check for updates
(Figure 2).

Figure 2: A query to force the Harmony
Hub to check for updates

The Harmony Hub sends its current firmware version to a Logitech
server to determine if an update is available (Figure 3). If an update
is available, the Logitech server sends a response containing a URL
for the new firmware version (Figure 4). Despite using a self-signed
certificate to intercept the HTTPS traffic sent by the Harmony Hub, we
were able to observe this process – demonstrating that the Harmony Hub
ignores invalid SSL certificates.

Figure 3: The Harmony Hub checks for
updates to its firmware

Figure 4: The server sends a response
with a URL for the updated firmware

We retrieved this firmware and examined the file. After extracting a
few layers of archives, the firmware can be found in the
harmony-image.squashfs file. This filesystem image is a SquashFS
filesystem compressed with lzma, a common format for embedded devices.
However, vendors often use old versions of squashfstools that are
incompatible with more recent squashfstools builds. We used the script included in firmware-mod-kit
to automate the process of finding the correct version of unsquashfs
to extract the filesystem image (Figure 5).

Figure 5: Using firmware-mod-kit to
extract the filesystem

With the filesystem contents extracted, we investigated some of the
configuration details of the Harmony Hub’s operating system.
Inspection revealed that various debug details were available in the
production image, such as kernel modules that were not stripped
(Figure 6).

Figure 6: Unstripped Linux kernel objects
on the filesystem

Investigation of /etc/passwd showed that the root user had no
password configured (Figure 7). Therefore, if we can enable the
dropbear SSH server, we can gain root access to the Harmony Hub
through SSH without a password.

Figure 7: /etc/passwd shows no password
is configured for the root user

We observed that an instance of a dropbear SSH server will be
enabled during initialization if the file /etc/tdeenable is present in
the filesystem (Figure 8).

Figure 8: A dropbear SSH server is
enabled by /etc/init.d/rcS script if /etc/tdeenable is present

Hijacking Update Process

During the initialization process, the Harmony Hub queries the
GetJson2Uris endpoint on the Logitech API to obtain a list of
URLs to use for various processes (Figure 9), such as the URL to use
when checking for updated firmware or a URL to obtain information
about updates’ additional software packages.

Figure 9: The request to obtain a list of
URL endpoints for various processes

We intercepted and modified the JSON object in the response from the
server to point the GetUpdates member to our own IP address, as
shown in Figure 10.

Figure 10: The modified JSON object member

Similar to the firmware update process, the Harmony Hub sends a POST
request to the endpoint specified by GetUpdates containing the
current versions of its internal software packages. The request shown
in Figure 11 contains a sample request for the HEOS package.

Figure 11: The JSON request object
containing the current version of the “HEOS” package

If the sysBuild parameter in the POST request body does not
match the current version known by the server, the server responds
with an initial response containing information about the new package
version. For an undetermined reason, the Harmony Hub ignores this
initial response and sends a second request. The second response
contains multiple URLs pointing to the updated package, as shown in
Figure 12.

Figure 12: The JSON response containing
URLs for the software update

We downloaded and inspected the .pkg files listed in the
response object, which are actually just ZIP archives. The archives
contain a simple file hierarchy, as shown in Figure 13.

Figure 13: The .pkg archive file hierarchy

The manifest.json file contains information used to instruct
the Harmony Hub’s update process on how to handle the archive’s
contents (Figure 14).

Figure 14: The contents of the
manifest.json file

The Harmony Hub’s update process executes the script provided by the
installer parameter of the manifest if it is present within the
archive. We modified this script, as shown in Figure 15, to create the
/etc/tdeenable file, which causes the boot process to enable
the SSH interface as previously described.

Figure 15: The modified file

We created a new malicious archive with the appropriate .pkg
extension, which was hosted on a local web server. The next time
the Harmony Hub checked for updates against the URL supplied in the
modified GetJson2URIs response, we sent a modified response to
point to this update. The Harmony Hub retrieved our malicious update
package, and after rebooting the Harmony Hub, the SSH interface was
enabled. This allowed us to access the device with the username
root and a blank password, as shown in Figure 16.

Figure 16: The SSH interface was enabled
after a reboot


As technology becomes further embedded into our daily lives, the
trust we place in various devices unknowingly increases exponentially.
Due to the fact that the Harmony Hub, like many IoT devcies, uses a
common processor architecture, malicious tools could easily be added
to a compromised Harmony Hub, increasing the overall impact of a
targeted attack. However, Logitech worked with our team to quickly
address the vulnerabilities with their current firmware, 4.15.96.
Developers of the devices we place our trust should be vigilant when
removing potential attack vectors that could expose end users to
security risks. We also want to share Logitech’s statement on the
research and work by the Red Team:

“At Logitech, we take our customers’ security and privacy very
seriously. In late January 2018, security research firm FireEye
pointed out vulnerabilities that could impact Logitech Harmony
Hub-based products*.

If a malicious hacker had already gained access to a Hub-users
network, these vulnerabilities could be exploited. We appreciate the
work that professional security research firms like FireEye provide
when identifying these types of vulnerabilities on IoT devices.

As soon as FireEye shared their research findings with us, we
reviewed internally and immediately started to develop firmware to
address it. As of April 10, we have released firmware that addresses
all of the vulnerabilities that were identified. For any customers who
haven’t yet updated to firmware version 4.15.96, we recommend you
check the MyHarmony software and sync your Hub-based remote and
receive it. Complete directions on updating your firmware can be
found here.

*Hub-based products include: Harmony Elite, Harmony Home Hub,
Harmony Ultimate Hub, harmony Hub, Harmony Home Control, Harmony Pro,
Harmony Smart Control, Harmony Companion, Harmony Smart Keyboard,
Harmony Ultimate and Ultimate Home.”

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