# CVE-2021-22543: Improper memory handling in Linux KVM

> Improper memory handling in Linux KVM allows local attackers to read/write random memory pages, leading to privilege escalation.

- **Severity:** High 8.7 (`CVSS:4.0/AV:L/AC:H/AT:N/PR:L/UI:N/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L`)
- **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:** Yes
- **Published:** 26 May 2021
- **Updated:** 16 Sep 2024
- **Also known as:** CLSA-2022-1659017902, CLSA-2022-1659018147, CLSA-2022-1669850228, CLSA-2022-1669919330, DEBIAN-CVE-2021-22543, RHSA-2021:3943, RHSA-2022:5640, UBUNTU-CVE-2021-22543

## What is CVE-2021-22543?

CVE-2021-22543 is a high-severity memory corruption vulnerability in Debian Debian Linux, published on 26 May 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

An issue was discovered in Linux: KVM through Improper handling of VM_IO|VM_PFNMAP vmas in KVM can bypass RO checks and can lead to pages being freed while still accessible by the VMM and guest. This allows users with the ability to start and control a VM to read/write random pages of memory and can result in local privilege escalation.

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

## Which versions are affected by CVE-2021-22543?

It affects 13 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `redhat-virtualization-host` | Red Hat:enterprise_linux:7::hypervisor | All versions | 0:4.3.19-20211013.0.el7_9 |
| `redhat-virtualization-host-image-update` | Red Hat:enterprise_linux:7::hypervisor | All versions | 0:4.3.19-20211013.0.el7_9 |
| `kernel` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-abi-whitelists` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-debug` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-debug-debuginfo` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-debug-devel` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-debuginfo` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-debuginfo-common-i686` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-debuginfo-common-s390x` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-debuginfo-common-x86_64` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-devel` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-doc` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-firmware` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-kdump` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-kdump-debuginfo` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `kernel-kdump-devel` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `perf` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `perf-debuginfo` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `python-perf` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |
| `python-perf-debuginfo` | Red Hat:rhel_els:6 | All versions | 0:2.6.32-754.48.1.el6 |

Products: Debian Debian Linux, Fedoraproject Fedora, Linux kernel, Netapp Cloud Backup, Netapp H300e Firmware, Netapp H300s Firmware, Netapp H410c Firmware, Netapp H410s Firmware, Netapp H500e Firmware, Netapp H500s Firmware, Netapp H700e Firmware, Netapp H700s Firmware, Netapp Solidfire Baseboard Management Controller Firmware.

## How do I fix CVE-2021-22543?

Apply the vendor's patch.

## Is CVE-2021-22543 being exploited?

There is no known exploitation of CVE-2021-22543 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-2021-22543 and fix it if it is affected.

What it is: CVE-2021-22543 is a high-severity memory corruption vulnerability in Debian Debian Linux, published on 26 May 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-2021-22543 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-2021-22543/ (Markdown: https://insights.sbomify.com/CVE-2021-22543/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-22543
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-22543
- OSV: https://osv.dev/vulnerability/CVE-2021-22543

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-22543/
Summaries are generated and may contain mistakes; the official description above is the record.