# CVE-2020-27821: Memory corruption in QEMU

> A guest user can crash the QEMU host process via an out-of-bounds write in the MSI-X table, causing denial of service.

- **Severity:** Medium 6.0 (`CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:N/I:N/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:** 8 Dec 2020
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2020-27821, GHSA-7p47-wfc3-mcqv, OESA-2021-1012, UBUNTU-CVE-2020-27821

## What is CVE-2020-27821?

CVE-2020-27821 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 8 Dec 2020. 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 memory management API of QEMU during the initialization of a memory region cache. This issue could lead to an out-of-bounds write access to the MSI-X table while performing MMIO operations. A guest user may abuse this flaw to crash the QEMU process on the host, resulting in a denial of service. This flaw affects QEMU versions prior to 5.2.0.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2020-27821?

It affects 2 products.


Products: Debian Debian Linux, Qemu Qemu.

## How do I fix CVE-2020-27821?

Upgrade to a fixed version.

## Is CVE-2020-27821 being exploited?

There is no known exploitation of CVE-2020-27821 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)
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- [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-2020-27821 and fix it if it is affected.

What it is: CVE-2020-27821 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 8 Dec 2020. 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-2020-27821 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-2020-27821/ (Markdown: https://insights.sbomify.com/CVE-2020-27821/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-27821
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-27821
- OSV: https://osv.dev/vulnerability/CVE-2020-27821

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-27821/
Summaries are generated and may contain mistakes; the official description above is the record.