Security Bulletin 27 Sep 2023

Insufficient authentication in the MQTT backend (broker) allows an attacker to access and even manipulate the telemetry data of the entire fleet of vehicles using the HopeChart HQT-401 telematics unit. Other models are possibly affected too.

Multiple vulnerabilities were identified:

- The MQTT backend does not require authentication, allowing unauthorized connections from an attacker.

- The vehicles publish their telemetry data (e.g. GPS Location, speed, odometer, fuel, etc) as messages in public topics. The backend also sends commands to the vehicles as MQTT posts in public topics. As a result, an attacker can access the confidential data of the entire fleet that is managed by the backend.

- The MQTT messages sent by the vehicles or the backend are not encrypted or authenticated. An attacker can create and post messages to impersonate a vehicle or the backend. The attacker could then, for example, send incorrect information to the backend about the vehicle's location.

- The backend can inject data into a vehicle´s CAN bus by sending a specific MQTT message on a public topic. Because these messages are not authenticated or encrypted, an attacker could impersonate the backend, create a fake message and inject CAN data in any vehicle managed by the backend.


The confirmed version is 201808021036, however further versions have been also identified as potentially impacted.

PCR14 is not in the list of PCRs that seal/unseal the “vault” key, but
due to the change that was implemented in commit
“7638364bc0acf8b5c481b5ce5fea11ad44ad7fd4”, fixing this issue alone would not solve the
problem of the config partition not being measured correctly.

Also, the “vault” key is sealed/unsealed with SHA1 PCRs instead of
SHA256.
This issue was somewhat mitigated due to all of the PCR extend functions
updating both the values of SHA256 and SHA1 for a given PCR ID.

However, due to the change that was implemented in commit
“7638364bc0acf8b5c481b5ce5fea11ad44ad7fd4”, this is no longer the case for PCR14, as
the code in “measurefs.go” explicitly updates only the SHA256 instance of PCR14, which
means that even if PCR14 were to be added to the list of PCRs sealing/unsealing the “vault”
key, changes to the config partition would still not be measured.

An attacker could modify the config partition without triggering the measured boot, this could
result in the attacker gaining full control over the device with full access to the contents of the
encrypted “vault”

Vault Key Sealed With SHA1 PCRs

The measured boot solution implemented in EVE OS leans on a PCR locking mechanism.

Different parts of the system update different PCR values in the TPM, resulting in a unique
value for each PCR entry.

These PCRs are then used in order to seal/unseal a key from the TPM which is used to
encrypt/decrypt the “vault” directory.

This “vault” directory is the most sensitive point in the system and as such, its content should
be protected.

This mechanism is noted in Zededa’s documentation as the “measured boot” mechanism,
designed to protect said “vault”.

The code that’s responsible for generating and fetching the key from the TPM assumes that
SHA256 PCRs are used in order to seal/unseal the key, and as such their presence is being
checked.

The issue here is that the key is not sealed using SHA256 PCRs, but using SHA1 PCRs.
This leads to several issues:

• Machines that have their SHA256 PCRs enabled but SHA1 PCRs disabled, as well
as not sealing their keys at all, meaning the “vault” is not protected from an attacker.

• SHA1 is considered insecure and reduces the complexity level required to unseal the
key in machines which have their SHA1 PCRs enabled.



An attacker can very easily retrieve the contents of the “vault”, which will effectively render
the “measured boot” mechanism meaningless.

In EVE OS, the “measured boot” mechanism prevents a compromised device from accessing
the encrypted data located in the vault.

As per the “measured boot” design, the PCR values calculated at different stages of the boot
process will change if any of their respective parts are changed.

This includes, among other things, the configuration of the bios, grub, the kernel cmdline,
initrd, and more.

However, this mechanism does not validate the entire rootfs, so an attacker can edit the
filesystem and gain control over the system.

As the default filesystem used by EVE OS is squashfs, this is somewhat harder than an ext4,
which is easily changeable.

This will not stop an attacker, as an attacker can repackage the squashfs with their changes
in it and replace the partition altogether.

This can also be done directly on the device, as the “003-storage-init” container contains the
“mksquashfs” and “unsquashfs” binaries (with the corresponding libs).

An attacker can gain full control over the device without changing the PCR values, thus not
triggering the “measured boot” mechanism, and having full access to the vault.

Note:

This issue was partially fixed in these commits (after disclosure to Zededa), where the config
partition measurement was added to PCR13:
• aa3501d6c57206ced222c33aea15a9169d629141
• 5fef4d92e75838cc78010edaed5247dfbdae1889.

This issue was made viable in version 9.0.0 when the calculation was moved to PCR14 but it was not included in the measured boot.

On boot, the Pillar eve container checks for the existence and content of
“/config/authorized_keys”.

If the file is present, and contains a supported public key, the container will go on to open
port 22 and enable sshd with the given keys as the authorized keys for root login.

An attacker could easily add their own keys and gain full control over the system without
triggering the “measured boot” mechanism implemented by EVE OS, and without marking
the device as “UUD” (“Unknown Update Detected”).

This is because the “/config” partition is not protected by “measured boot”, it is mutable, and
it is not encrypted in any way.

An attacker can gain full control over the device without changing the PCR values, thus not
triggering the “measured boot” mechanism, and having full access to the vault.

Note:

This issue was partially fixed in these commits (after disclosure to Zededa), where the config
partition measurement was added to PCR13:

• aa3501d6c57206ced222c33aea15a9169d629141

• 5fef4d92e75838cc78010edaed5247dfbdae1889.

This issue was made viable in version 9.0.0 when the calculation was moved to PCR14 but it was not included in the measured boot.

Due to the implementation of "deriveVaultKey", prior to version 7.10, the generated vault key
would always have the last 16 bytes predetermined to be "arfoobarfoobarfo".

This issue happens because "deriveVaultKey" calls "retrieveCloudKey" (which will always
return "foobarfoobarfoobarfoobarfoobarfo" as the key), and then merges the 32byte
randomly generated key with this key (by takeing 16bytes from each, see "mergeKeys").

This makes the key a lot weaker.

This issue does not persist in devices that were initialized on/after version 7.10, but devices
that were initialized before that and updated to a newer version still have this issue.

Roll an update that enforces the full 32bytes key usage.

Improper Restriction of XML External Entity Reference vulnerability in MIM Assistant and Client DICOM RTst Loading modules allows XML Entity Linking / XML External Entities Blowup.

In order to take advantage of this vulnerability, an attacker must
craft a malicious XML document, embed this document into specific 3rd
party private RTst metadata tags, transfer the now compromised
DICOM object to MIM, and force MIM to archive and load the data.

Users on either version are strongly encouraged to update to an unaffected version (7.2.11+, 7.3.4+).

This issue was found and analyzed by MIM Software's internal security team.  We are unaware of any proof of concept or actual exploit available in the wild.

For more information, visit https://www.mimsoftware.com/cve-2023-3892 https://www.mimsoftware.com/cve-2023-3892

This issue affects MIM Assistant: 7.2.10, 7.3.3; MIM Client: 7.2.10, 7.3.3.