# CVE-2021-3653: Privilege escalation in kernel

> A malicious L1 guest can escape to the host via improper validation in KVM's AMD SVM nested virtualization, enabling host code execution or data leaks.

- **Severity:** High 8.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H`)
- **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:** 29 Sep 2021
- **Updated:** 3 Aug 2024
- **Also known as:** ALSA-2021:3548, AZL-6575, DEBIAN-CVE-2021-3653, GHSA-g58x-c6rr-7fp2, RHSA-2021:3547, RHSA-2021:3548, RLSA-2021:3547, RLSA-2021:3548, UBUNTU-CVE-2021-3653, USN-5062-1

## What is CVE-2021-3653?

CVE-2021-3653 is a high-severity vulnerability in Debian Debian Linux, published on 29 Sep 2021. 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 KVM's AMD code for supporting SVM nested virtualization. The flaw occurs when processing the VMCB (virtual machine control block) provided by the L1 guest to spawn/handle a nested guest (L2). Due to improper validation of the "int_ctl" field, this issue could allow a malicious L1 to enable AVIC support (Advanced Virtual Interrupt Controller) for the L2 guest. As a result, the L2 guest would be allowed to read/write physical pages of the host, resulting in a crash of the entire system, leak of sensitive data or potential guest-to-host escape. This flaw affects Linux kernel versions prior to 5.14-rc7.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2021-3653?

It affects 3 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `kernel-tools-libs-devel` | AlmaLinux:8 | All versions | 4.18.0-305.19.1.el8_4 |
| `bpftool` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `bpftool-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-abi-stablelists` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-core` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-cross-headers` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debug` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debug-core` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debug-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debug-devel` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debug-modules` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debug-modules-extra` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debuginfo-common-aarch64` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debuginfo-common-ppc64le` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debuginfo-common-s390x` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debuginfo-common-x86_64` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-devel` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-doc` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-modules` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-modules-extra` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-tools` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-tools-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-tools-libs` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-zfcpdump` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-zfcpdump-core` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-zfcpdump-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-zfcpdump-devel` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-zfcpdump-modules` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-zfcpdump-modules-extra` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `perf` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `perf-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `python3-perf` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `python3-perf-debuginfo` | Red Hat:enterprise_linux:8::baseos | All versions | 0:4.18.0-305.19.1.el8_4 |
| `bpftool-debuginfo` | Red Hat:enterprise_linux:8::crb | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debug-debuginfo` | Red Hat:enterprise_linux:8::crb | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debuginfo` | Red Hat:enterprise_linux:8::crb | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debuginfo-common-aarch64` | Red Hat:enterprise_linux:8::crb | All versions | 0:4.18.0-305.19.1.el8_4 |
| `kernel-debuginfo-common-ppc64le` | Red Hat:enterprise_linux:8::crb | All versions | 0:4.18.0-305.19.1.el8_4 |

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

## How do I fix CVE-2021-3653?

Apply the vendor's patch.

## Is CVE-2021-3653 being exploited?

There is no known exploitation of CVE-2021-3653 in the wild and no public exploit code.

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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-2021-3653 and fix it if it is affected.

What it is: CVE-2021-3653 is a high-severity vulnerability in Debian Debian Linux, published on 29 Sep 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-2021-3653 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-2021-3653/ (Markdown: https://insights.sbomify.com/CVE-2021-3653/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3653
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3653
- OSV: https://osv.dev/vulnerability/CVE-2021-3653

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3653/
Summaries are generated and may contain mistakes; the official description above is the record.