Upstream information

CVE-2023-43635 at MITRE

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.





SUSE information

Overall state of this security issue: Resolved

This issue is currently rated as having important severity.

CVSS v3 Scores
CVSS detail National Vulnerability Database
Base Score 8.8
Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Attack Vector Local
Attack Complexity Low
Privileges Required Low
User Interaction None
Scope Changed
Confidentiality Impact High
Integrity Impact High
Availability Impact High
CVSSv3 Version 3.1
No SUSE Bugzilla entries cross referenced.

SUSE Security Advisories:

List of released packages

Product(s) Fixed package version(s) References

Status of this issue by product and package

Please note that this evaluation state might be work in progress, incomplete or outdated. Also information for service packs in the LTSS phase is only included for issues meeting the LTSS criteria. If in doubt, feel free to contact us for clarification. The updates are grouped by state of their lifecycle. SUSE product lifecycles are documented on the lifecycle page.

Product(s) Source package State
Products under general support and receiving all security fixes.
openSUSE Leap 15.6 govulncheck-vulndb Released
Products past their end of life and not receiving proactive updates anymore.
SUSE Linux Enterprise Module for Package Hub 15 SP5 govulncheck-vulndb Affected
SUSE Linux Enterprise Module for Package Hub 15 SP6 govulncheck-vulndb Affected
openSUSE Leap 15.5 govulncheck-vulndb Affected

SUSE Timeline for this CVE

CVE page created: Wed Sep 20 18:00:51 2023
CVE page last modified: Wed Mar 4 19:13:34 2026