# CVE-2021-4207: Memory corruption in QEMU

> A malicious privileged guest user can trigger a heap-based buffer overflow in QEMU's QXL emulation to execute arbitrary code or crash the host.

- **Severity:** High 8.2 (`CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Apr 2022
- **Updated:** 21 Mar 2025
- **Also known as:** AZL-35155, AZL-9619, DEBIAN-CVE-2021-4207, GHSA-9p8r-v33g-4939, UBUNTU-CVE-2021-4207

## What is CVE-2021-4207?

CVE-2021-4207 is a high-severity memory corruption vulnerability in Debian Debian Linux, published on 29 Apr 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A flaw was found in the QXL display device emulation in QEMU. A double fetch of guest controlled values `cursor->header.width` and `cursor->header.height` can lead to the allocation of a small cursor object followed by a subsequent heap-based buffer overflow. A malicious privileged guest user could use this flaw to crash the QEMU process on the host or potentially execute arbitrary code within the context of the QEMU process.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2021-4207?

It affects 3 products.


Products: Debian Debian Linux, Qemu Qemu, Redhat Enterprise Linux.

## How do I fix CVE-2021-4207?

Apply the vendor's patch.

## Is CVE-2021-4207 being exploited?

There is no known exploitation of CVE-2021-4207 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-4207 and fix it if it is affected.

What it is: CVE-2021-4207 is a high-severity memory corruption vulnerability in Debian Debian Linux, published on 29 Apr 2022. 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-2021-4207 in the wild and no public exploit code.

Affected product: Debian Debian Linux. 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-2021-4207/ (Markdown: https://insights.sbomify.com/CVE-2021-4207/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-4207
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-4207
- OSV: https://osv.dev/vulnerability/CVE-2021-4207

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-4207/
Summaries are generated and may contain mistakes; the official description above is the record.