# CVE-2021-20219: Denial of service in kernel

> A local attacker can cause a denial of service in the Linux kernel by exploiting a missing sanity check in the TTY driver.

- **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:** 23 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-4x74-wx76-5j5h, UBUNTU-CVE-2021-20219

## What is CVE-2021-20219?

CVE-2021-20219 is a medium-severity denial of service vulnerability in Linux kernel, 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

A denial of service vulnerability was found in n_tty_receive_char_special in drivers/tty/n_tty.c of the Linux kernel. In this flaw a local attacker with a normal user privilege could delay the loop (due to a changing ldata->read_head, and a missing sanity check) and cause a threat to the system availability.

Weakness: CWE-697 (Incorrect Comparison)

## Which versions are affected by CVE-2021-20219?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-20219?

Apply the vendor's patch.

## Is CVE-2021-20219 being exploited?

There is no known exploitation of CVE-2021-20219 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20219 and fix it if it is affected.

What it is: CVE-2021-20219 is a medium-severity denial of service vulnerability in Linux kernel, 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-2021-20219 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2021-20219/ (Markdown: https://insights.sbomify.com/CVE-2021-20219/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20219
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20219
- OSV: https://osv.dev/vulnerability/CVE-2021-20219

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-20219/
Summaries are generated and may contain mistakes; the official description above is the record.