# CVE-2021-47008: KVM: SVM: Make sure GHCB is mapped before updating

> A missing check in the Linux kernel KVM SVM module allows a local attacker to trigger a NULL pointer dereference, causing a system crash.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** No
- **Published:** 28 Feb 2024
- **Updated:** 11 May 2026
- **Also known as:** GHSA-9pjj-2jvj-24rm, UBUNTU-CVE-2021-47008

## What is CVE-2021-47008?

CVE-2021-47008 is a medium-severity vulnerability in Linux kernel, published on 28 Feb 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

KVM: SVM: Make sure GHCB is mapped before updating

Access to the GHCB is mainly in the VMGEXIT path and it is known that the
GHCB will be mapped. But there are two paths where it is possible the GHCB
might not be mapped.

The sev_vcpu_deliver_sipi_vector() routine will update the GHCB to inform
the caller of the AP Reset Hold NAE event that a SIPI has been delivered.
However, if a SIPI is performed without a corresponding AP Reset Hold,
then the GHCB might not be mapped (depending on the previous VMEXIT),
which will result in a NULL pointer dereference.

The svm_complete_emulated_msr() routine will update the GHCB to inform
the caller of a RDMSR/WRMSR operation about any errors. While it is likely
that the GHCB will be mapped in this situation, add a safe guard
in this path to be certain a NULL pointer dereference is not encountered.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2021-47008?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47008?

No fix has been published for CVE-2021-47008 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-47008 being exploited?

There is no known exploitation of CVE-2021-47008 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-47008 and fix it if it is affected.

What it is: CVE-2021-47008 is a medium-severity vulnerability in Linux kernel, published on 28 Feb 2024. 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-2021-47008 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2021-47008/ (Markdown: https://insights.sbomify.com/CVE-2021-47008/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47008
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47008
- OSV: https://osv.dev/vulnerability/CVE-2021-47008

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47008/
Summaries are generated and may contain mistakes; the official description above is the record.