CVE-2023-43635: lf-edge, zededa eve os Use of Weak Hash

Vulnerability summary

CVE-2023-43635 is a high (CVSS 8.8) Use of Weak Hash vulnerability in lf-edge, zededa eve os. EPSS estimates a 0.12% chance of exploitation in the next 30 days, higher than 1.5% of scored vulnerabilities.

Timeline

1. 20-09-2023
   PublishedVulnerability first disclosed.
2. 25-09-2024
   Last modifiedVulnerability information updated.

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 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.

• CWE-328Use of Weak HashThe product uses an algorithm that produces a digest (output value) that does not meet security expectations for a hash function that allows an adversary to reasonably determine the original input (preimage attack), find another input that can produce the same hash (2nd preimage attack), or find multiple inputs that evaluate to the same hash (birthday attack).
• CWE-522Insufficiently Protected CredentialsThe product transmits or stores authentication credentials, but it uses an insecure method that is susceptible to unauthorized interception and/or retrieval.
• CWE-327Use of a Broken or Risky Cryptographic AlgorithmThe product uses a broken or risky cryptographic algorithm or protocol.