CVE-2023-43636

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.