SSH as Root Unlockable Without Triggering 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.