# CVE-2021-33630: NULL-ptr-deref in network sched

> A NULL pointer dereference in the Linux kernel network scheduler allows attackers to cause a denial of service.

- **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:** 18 Jan 2024
- **Updated:** 7 May 2025
- **Also known as:** DEBIAN-CVE-2021-33630, GHSA-4mwf-4888-4x35, UBUNTU-CVE-2021-33630

## What is CVE-2021-33630?

CVE-2021-33630 is a medium-severity vulnerability in openEuler kernel, published on 18 Jan 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

NULL Pointer Dereference vulnerability in openEuler kernel on Linux (network modules) allows Pointer Manipulation. This vulnerability is associated with program files net/sched/sch_cbs.C.

This issue affects openEuler kernel: from 4.19.90 before 4.19.90-2401.3.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2021-33630?

It affects 1 product.


Products: Openatom Openeuler.

## How do I fix CVE-2021-33630?

Apply the vendor's patch.

## Is CVE-2021-33630 being exploited?

There is no known exploitation of CVE-2021-33630 in the wild and no public exploit code.

## Other vulnerabilities in openEuler kernel

- [CVE-2021-33631](https://insights.sbomify.com/CVE-2021-33631/): Kernel crash in EXT4 filesystem (medium 5.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-33630 and fix it if it is affected.

What it is: CVE-2021-33630 is a medium-severity vulnerability in openEuler kernel, published on 18 Jan 2024. 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-2021-33630 in the wild and no public exploit code.

Affected product: openEuler 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-2021-33630/ (Markdown: https://insights.sbomify.com/CVE-2021-33630/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-33630
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-33630
- OSV: https://osv.dev/vulnerability/CVE-2021-33630

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-33630/
Summaries are generated and may contain mistakes; the official description above is the record.