CVE-2023-43635

CVE-2023-43635 is a high-severity vulnerability in Linuxfoundation Edge Virtualization Engine with a CVSS 3.x base score of 8.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-327.

Key facts

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.

Frequently asked questions

What is CVE-2023-43635?
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.
How severe is CVE-2023-43635?
CVE-2023-43635 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2023-43635 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (2nd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-43635?
CVE-2023-43635 affects Linuxfoundation Edge Virtualization Engine. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2023-43635?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2023-43635 published?
CVE-2023-43635 was published on 2023-09-20 and last updated on 2026-06-17.

References

Affected products (1)

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