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In EVE OS, the “measured boot” mechanism prevents a...

High severity Unreviewed Published Sep 20, 2023 to the GitHub Advisory Database • Updated Apr 4, 2024

Package

No package listedSuggest a package

Affected versions

Unknown

Patched versions

Unknown

Description

In EVE OS, the “measured boot” mechanism prevents a compromised device from accessing
the encrypted data located in the vault.

As per the “measured boot” design, the PCR values calculated at different stages of the boot
process will change if any of their respective parts are changed.

This includes, among other things, the configuration of the bios, grub, the kernel cmdline,
initrd, and more.

However, this mechanism does not validate the entire rootfs, so an attacker can edit the
filesystem and gain control over the system.

As the default filesystem used by EVE OS is squashfs, this is somewhat harder than an ext4,
which is easily changeable.

This will not stop an attacker, as an attacker can repackage the squashfs with their changes
in it and replace the partition altogether.

This can also be done directly on the device, as the “003-storage-init” container contains the
“mksquashfs” and “unsquashfs” binaries (with the corresponding libs).

An attacker can gain full control over the device without changing the PCR values, thus not
triggering the “measured boot” mechanism, and having full access to the vault.

Note:

This issue was partially fixed in these commits (after disclosure to Zededa), where the config
partition measurement was added to PCR13:

• aa3501d6c57206ced222c33aea15a9169d629141

• 5fef4d92e75838cc78010edaed5247dfbdae1889.

This issue was made viable in version 9.0.0 when the calculation was moved to PCR14 but it was not included in the measured boot.

References

Published by the National Vulnerability Database Sep 20, 2023
Published to the GitHub Advisory Database Sep 20, 2023
Last updated Apr 4, 2024

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

EPSS score

0.043%
(10th percentile)

Weaknesses

CVE ID

CVE-2023-43636

GHSA ID

GHSA-x9mp-jm4h-jjf8

Source code

No known source code

Dependabot alerts are not supported on this advisory because it does not have a package from a supported ecosystem with an affected and fixed version.

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