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.
Understanding This Vulnerability
This Common Vulnerabilities and Exposures (CVE) entry provides detailed information about a security vulnerability that has been publicly disclosed. CVEs are standardized identifiers assigned by MITRE Corporation to track and catalog security vulnerabilities across software and hardware products.
The severity rating (HIGH) indicates the potential impact of this vulnerability based on the CVSS (Common Vulnerability Scoring System) framework. Higher severity ratings typically indicate vulnerabilities that could lead to more significant security breaches if exploited. Security teams should prioritize remediation efforts based on severity, exploit availability, and the EPSS (Exploit Prediction Scoring System) score, which predicts the likelihood of exploitation in the wild.
If this vulnerability affects products or systems in your infrastructure, we recommend reviewing the affected products section, checking for available patches or updates from vendors, and implementing recommended workarounds or solutions until a permanent fix is available. Organizations should also monitor security advisories and threat intelligence feeds for updates about active exploitation of this vulnerability.