CVE-2023-43631: SSH as Root Unlockable Without Triggering Measured Boot
Impact
On boot, the Pillar container checks for /config/authorizedkeys. If present with a valid public key, it enables SSH on port 22 with root login. The /config partition is not protected by measured boot, is mutable and unencrypted.
This enables an attacker with physical access to the device to take out the disk, modify the /config partition using a separate server, then insert it, without the inserted key being flagged as an integrity voilation my measured boot and remote attestation.
Patches
Patched in 9.4.3-lts
Workarounds
None (apart from preventing physical access to the device)
Other sources
On boot, the Pillar eve container checks for the existence and content of “/config/authorizedkeys”.
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.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is CVE-2023-43631?
CVE-2023-43631 refers to a vulnerability in the Pillar eve container that allows an attacker to unlock SSH as root without triggering measured boot.
What is the severity of CVE-2023-43631?
The severity of CVE-2023-43631 is high, with a severity value of 8.8.
Which software is affected by CVE-2023-43631?
The Linuxfoundation Edge Virtualization Engine versions 8.6.0 up to exclusive 9.5.0 are affected by CVE-2023-43631.
How does CVE-2023-43631 work?
CVE-2023-43631 exploits the presence and content of the '/config/authorized_keys' file in the Pillar eve container to enable root login via SSH without triggering measured boot.
Is there a fix for CVE-2023-43631?
Currently, there is no known fix for CVE-2023-43631. It is recommended to follow the provided reference for any updates or patches.