On boot, the Pillar eve container checks for the existence and content of
“/config/GlobalConfig/global.json”.
If the file exists, it overrides the existing configuration on the device on boot.
This allows an attacker to change the system’s configuration, which also includes some
debug functions.
This could be used to unlock the ssh with custom “authorized_keys” via the
“debug.enable.ssh” key, similar to the “authorized_keys” finding that was noted before.
Other usages include unlocking the usb to enable the keyboard via the “debug.enable.usb”
key, allowing VNC access via the “app.allow.vnc” key, and more.
An attacker could easily enable these debug functionalities 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, thereby 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.
CVSS Score
8.8
EPSS Score
0.0
Published
2023-09-21
When sealing/unsealing the “vault” key, a list of PCRs is used, which defines which PCRs
are used.
In a previous project, CYMOTIVE found that the configuration is not protected by the secure
boot, and in response Zededa implemented measurements on the config partition that was
mapped to PCR 13.
In that process, PCR 13 was added to the list of PCRs that seal/unseal the key.
In commit “56e589749c6ff58ded862d39535d43253b249acf”, the config partition
measurement moved from PCR 13 to PCR 14, but PCR 14 was not added to the list of
PCRs that seal/unseal the key.
This change makes the measurement of PCR 14 effectively redundant as it would not affect
the sealing/unsealing of the key.
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”
CVSS Score
8.8
EPSS Score
0.0
Published
2023-09-21