# What is CVE-2023-43635?

> CVE-2023-43635 is a high-severity flaw (CVSS 8.8) in Edge Virtualization Engine from Linuxfoundation, published on 20 September 2023. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 0.1%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2023-43635

## At a glance

- **Verdict:** Plan it in. No sign of exploitation and a low forecast. Patch it in your normal update cycle.
- **Precursor Intelligence risk score:** 46 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** High (CVSS 8.8 out of 10)
- **Known to be exploited:** No, not on the list of flaws known to be exploited today
- **Chance of use in the next 30 days:** 0.1% (latest exploit-likelihood forecast)
- **Published:** 20 September 2023
- **Record last updated:** 28 September 2023
- **Main product:** Edge Virtualization Engine from Linuxfoundation
- **Affected products:** 1

## What is CVE-2023-43635? In plain terms

An attacker has to be already on the device with an ordinary user account, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

### The 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.

### What kind of flaw is it?

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

### How an attack on it works

- Where an attacker can be: Already on the device
- How hard it is to pull off: Easy: no special conditions
- Login needed first: An ordinary user account
- Does someone have to click: No, nobody has to do anything
- What an attacker gets: Can read data, change data and take it offline

Severity vector: `CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`

## Is CVE-2023-43635 being exploited? Not that we know of

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 0.1%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 0.1%, 0.1%, 0.1%, 0.1%, 0.1%, 0.1%, 0.1%.

### Timeline

- 20 September 2023: Published
- 28 September 2023: Record last updated

### How Precursor Intelligence ranks it

CVE-2023-43635 scores **46 out of 100 (Medium)**, with the action "Plan remediation".

Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less:

- Evidence it is being exploited: biggest factor
- How severe it is: strong factor
- How widely exposed it is: key context
- Real threat activity around it: key context

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it.

## Who is affected by CVE-2023-43635?

The published record lists 1 product. Versions are as published: "before 9.5.0" means every version up to, but not including, 9.5.0.

- [Edge Virtualization Engine](https://www.precursorintelligence.com/product/linuxfoundation/edge_virtualization_engine) by [Linuxfoundation](https://www.precursorintelligence.com/vendors/linuxfoundation) (Operating system): before 9.5.0

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

1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
2. **Apply the vendor’s fix.** Install the latest update from the vendor. The references list where the vendor has published details.
3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood.

### References

- [asrg.io](https://asrg.io/security-advisories/cve-2023-43635/)

## Questions

### What is CVE-2023-43635?

CVE-2023-43635 is a high-severity flaw in Edge Virtualization Engine from Linuxfoundation, published on 20 September 2023. An attacker has to be already on the device with an ordinary user account, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

### How serious is CVE-2023-43635?

It scores 8.8 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2023-43635 is 46 out of 100, which is Medium. Its action is "Plan remediation". No sign of exploitation and a low forecast. Patch it in your normal update cycle.

### Is CVE-2023-43635 being exploited?

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 0.1%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2023-43635 affect?

For Edge Virtualization Engine from Linuxfoundation: before 9.5.0.

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

Install the update the vendor names in its advisory. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.

## Does CVE-2023-43635 affect you?

Precursor Intelligence keeps checking for you:

- **Tell us what you run.** Pick your software from a list, or let us work it out from your website.
- **We match it to every flaw.** Over 400,000 published flaws, checked against your list.
- **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it.
- **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools.

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