# CVE-2021-3679: Denial of service in kernel

> Privileged local users can cause a denial of service by exhausting CPU resources in the Linux kernel tracing module.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 5 Aug 2021
- **Updated:** 3 Aug 2024
- **Also known as:** AZL-6577, DEBIAN-CVE-2021-3679, GHSA-mfgx-frfq-59jc, UBUNTU-CVE-2021-3679

## What is CVE-2021-3679?

CVE-2021-3679 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 5 Aug 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A lack of CPU resource in the Linux kernel tracing module functionality in versions prior to 5.14-rc3 was found in the way user uses trace ring buffer in a specific way. Only privileged local users (with CAP_SYS_ADMIN capability) could use this flaw to starve the resources causing denial of service.

Weakness: CWE-835 (Loop with Unreachable Exit Condition), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2021-3679?

It affects 3 products.


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

## How do I fix CVE-2021-3679?

Upgrade to a fixed version.

## Is CVE-2021-3679 being exploited?

There is no known exploitation of CVE-2021-3679 in the wild and no public exploit code.

Public exploit code:

- Exploitation for CVE-2021-3679 and document for its fix (github_poc): https://github.com/aegistudio/RingBufferDetonator

## 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-2021-3679 and fix it if it is affected.

What it is: CVE-2021-3679 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 5 Aug 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-2021-3679 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-2021-3679/ (Markdown: https://insights.sbomify.com/CVE-2021-3679/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3679
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3679
- OSV: https://osv.dev/vulnerability/CVE-2021-3679

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3679/
Summaries are generated and may contain mistakes; the official description above is the record.