# CVE-2021-33656: Memory corruption in openEuler:kernel

> A local attacker can trigger an out-of-bounds write in the kernel via a malicious ioctl command, potentially leading to code execution or privilege escalation.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Jul 2022
- **Updated:** 8 Oct 2026
- **Also known as:** DEBIAN-CVE-2021-33656, GHSA-9p9r-j677-3r3q, OESA-2022-1748, UBUNTU-CVE-2021-33656, USN-5591-1, USN-5591-2, USN-5591-3, USN-5591-4, USN-5597-1, USN-5598-1

## What is CVE-2021-33656?

CVE-2021-33656 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 18 Jul 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

When setting font with malicous data by ioctl cmd PIO_FONT,kernel will write memory out of bounds.

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

## Which versions are affected by CVE-2021-33656?

It affects 3 products.


Products: Debian Debian Linux, Linux kernel, Openatom Openeuler.

## How do I fix CVE-2021-33656?

Apply the vendor's patch.

## Is CVE-2021-33656 being exploited?

There is no known exploitation of CVE-2021-33656 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-2021-33656 and fix it if it is affected.

What it is: CVE-2021-33656 is a medium-severity memory corruption vulnerability in Debian Debian Linux, published on 18 Jul 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-2021-33656 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-2021-33656/ (Markdown: https://insights.sbomify.com/CVE-2021-33656/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-33656
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-33656
- OSV: https://osv.dev/vulnerability/CVE-2021-33656

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-33656/
Summaries are generated and may contain mistakes; the official description above is the record.