# CVE-2021-3409: Memory corruption in QEMU

> A malicious privileged guest can crash the QEMU host or execute code due to ineffective patches for out-of-bounds access in SDHCI emulation.

- **Severity:** Medium 5.7 (`CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:L`)
- **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:** 23 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-3409, GHSA-mx4g-vhmg-3rf6, UBUNTU-CVE-2021-3409

## What is CVE-2021-3409?

CVE-2021-3409 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 23 Mar 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

The patch for CVE-2020-17380/CVE-2020-25085 was found to be ineffective, thus making QEMU vulnerable to the out-of-bounds read/write access issues previously found in the SDHCI controller emulation code. This flaw allows a malicious privileged guest to crash the QEMU process on the host, resulting in a denial of service or potential code execution. QEMU up to (including) 5.2.0 is affected by this.

Weakness: CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2021-3409?

It affects 4 products.


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

## How do I fix CVE-2021-3409?

Apply the vendor's patch.

## Is CVE-2021-3409 being exploited?

There is no known exploitation of CVE-2021-3409 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-2021-3409 and fix it if it is affected.

What it is: CVE-2021-3409 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 23 Mar 2021. 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-2021-3409 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-2021-3409/ (Markdown: https://insights.sbomify.com/CVE-2021-3409/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3409
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3409
- OSV: https://osv.dev/vulnerability/CVE-2021-3409

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3409/
Summaries are generated and may contain mistakes; the official description above is the record.