# CVE-2018-20784: Denial of service in n/a

> Attackers can cause a denial of service via an infinite loop in the Linux kernel scheduler by inducing high load.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Feb 2019
- **Updated:** 5 Aug 2024
- **Also known as:** DEBIAN-CVE-2018-20784, GHSA-qg2g-rfcv-qffx, UBUNTU-CVE-2018-20784

## What is CVE-2018-20784?

CVE-2018-20784 is a critical denial of service vulnerability in Canonical Ubuntu Linux, published on 22 Feb 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel before 4.20.2, kernel/sched/fair.c mishandles leaf cfs_rq's, which allows attackers to cause a denial of service (infinite loop in update_blocked_averages) or possibly have unspecified other impact by inducing a high load.

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2018-20784?

It affects 4 products.


Products: Canonical Ubuntu Linux, Linux kernel, Redhat Enterprise Linux, Redhat Enterprise Linux for Real Time.

## How do I fix CVE-2018-20784?

Apply the vendor's patch.

## Is CVE-2018-20784 being exploited?

There is no known exploitation of CVE-2018-20784 in the wild and no public exploit code.

## Other vulnerabilities in Canonical Ubuntu Linux

- [CVE-2020-11651](https://insights.sbomify.com/CVE-2020-11651/): SaltStack Salt Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2020-7247](https://insights.sbomify.com/CVE-2020-7247/): OpenSMTPD Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2019-16928](https://insights.sbomify.com/CVE-2019-16928/): Exim Out-of-bounds Write (critical 9.8, exploited in the wild)
- [CVE-2018-6789](https://insights.sbomify.com/CVE-2018-6789/): Exim Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2015-2590](https://insights.sbomify.com/CVE-2015-2590/): Oracle Java SE and Java SE Embedded Remote Code Execution (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-20784 and fix it if it is affected.

What it is: CVE-2018-20784 is a critical denial of service vulnerability in Canonical Ubuntu Linux, published on 22 Feb 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2018-20784 in the wild and no public exploit code.

Affected product: Canonical Ubuntu 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-2018-20784/ (Markdown: https://insights.sbomify.com/CVE-2018-20784/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-20784
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-20784
- OSV: https://osv.dev/vulnerability/CVE-2018-20784

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-20784/
Summaries are generated and may contain mistakes; the official description above is the record.