CVE-2023-43635

/// Technical description

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 th

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References