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 their keys at all, meaning the “vault” is not protected from an attacker.
• SHA1 is considered insecure and reduces the complexity level required to unseal the key in machines which have their SHA1 PCRs enabled.
An attacker can very easily retrieve the contents of the “vault”, which will effectively render the “measured boot” mechanism meaningless.
The product uses a broken or risky cryptographic algorithm or protocol.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Edge_virtualization_engine | Linuxfoundation | * | 9.5.0 (excluding) |
Cryptographic algorithms are the methods by which data is scrambled to prevent observation or influence by unauthorized actors. Insecure cryptography can be exploited to expose sensitive information, modify data in unexpected ways, spoof identities of other users or devices, or other impacts. It is very difficult to produce a secure algorithm, and even high-profile algorithms by accomplished cryptographic experts have been broken. Well-known techniques exist to break or weaken various kinds of cryptography. Accordingly, there are a small number of well-understood and heavily studied algorithms that should be used by most products. Using a non-standard or known-insecure algorithm is dangerous because a determined adversary may be able to break the algorithm and compromise whatever data has been protected. Since the state of cryptography advances so rapidly, it is common for an algorithm to be considered “unsafe” even if it was once thought to be strong. This can happen when new attacks are discovered, or if computing power increases so much that the cryptographic algorithm no longer provides the amount of protection that was originally thought. For a number of reasons, this weakness is even more challenging to manage with hardware deployment of cryptographic algorithms as opposed to software implementation. First, if a flaw is discovered with hardware-implemented cryptography, the flaw cannot be fixed in most cases without a recall of the product, because hardware is not easily replaceable like software. Second, because the hardware product is expected to work for years, the adversary’s computing power will only increase over time.