# CVE-2023-43635: Vault Key Sealed With SHA1 PCRs

> Attackers can bypass measured boot protections and read sensitive vault data because the TPM key is sealed with insecure SHA1 PCRs instead of SHA256.

- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Sep 2023
- **Updated:** 25 Sep 2024
- **Also known as:** GHSA-4jvr-vj2c-8q37, GO-2026-4434

## What is CVE-2023-43635?

CVE-2023-43635 is a high-severity vulnerability in EVE OS, published on 20 Sep 2023. It can only be exploited from the same machine or local network, with no action from the victim.

### Official 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.

Weakness: CWE-327 (Use of a Broken or Risky Cryptographic Algorithm), CWE-522 (Insufficiently Protected Credentials), CWE-328 (Use of Weak Hash)

## Which versions are affected by CVE-2023-43635?

3 open source packages ship an affected version, including github.com/lf-edge/eve. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/lf-edge/eve` | Go | All versions | 0.0.0-20230519072751-977f42b07fa9 |
| `github.com/lf-edge/eve` | Go | All versions | 0.0.0-20230519072751-977f42b07fa9 |
| `github.com/lf-edge/eve` | Go | All versions | 0.0.0-20230519072751-977f42b07fa9 |

Products: Linuxfoundation Edge Virtualization Engine.

## How do I fix CVE-2023-43635?

Upgrade github.com/lf-edge/eve to 0.0.0-20230519072751-977f42b07fa9 or later.

## Is CVE-2023-43635 being exploited?

There is no known exploitation of CVE-2023-43635 in the wild and no public exploit code.

## Other vulnerabilities in EVE OS

- [CVE-2023-43632](https://insights.sbomify.com/CVE-2023-43632/): Freely Allocate Buffer on The Stack With Data From Socket (critical 9.0)
- [CVE-2023-43631](https://insights.sbomify.com/CVE-2023-43631/): SSH as Root Unlockable Without Triggering Measured Boot (high 8.8)
- [CVE-2023-43630](https://insights.sbomify.com/CVE-2023-43630/): Config Partition Not Measured From 2 Fronts (high 8.8)
- [CVE-2023-43636](https://insights.sbomify.com/CVE-2023-43636/): Rootfs Not Protected (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-43635 and fix it if it is affected.

What it is: CVE-2023-43635 is a high-severity vulnerability in EVE OS, published on 20 Sep 2023. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-43635 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/lf-edge/eve (Go): affected all versions; fixed in 0.0.0-20230519072751-977f42b07fa9
- github.com/lf-edge/eve (Go): affected all versions; fixed in 0.0.0-20230519072751-977f42b07fa9
- github.com/lf-edge/eve (Go): affected all versions; fixed in 0.0.0-20230519072751-977f42b07fa9

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-43635/ (Markdown: https://insights.sbomify.com/CVE-2023-43635/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-43635
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-43635
- OSV: https://osv.dev/vulnerability/CVE-2023-43635

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-43635/
Summaries are generated and may contain mistakes; the official description above is the record.