# CVE-2021-3739: Null dereference in kernel

> A local attacker with CAP_SYS_ADMIN can trigger a NULL pointer dereference in the btrfs filesystem, causing a system crash or leaking kernel information.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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:** 7 Mar 2022
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-3739, UBUNTU-CVE-2021-3739

## What is CVE-2021-3739?

CVE-2021-3739 is a high-severity vulnerability in Fedoraproject Fedora, published on 7 Mar 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A NULL pointer dereference flaw was found in the btrfs_rm_device function in fs/btrfs/volumes.c in the Linux Kernel, where triggering the bug requires ‘CAP_SYS_ADMIN’. This flaw allows a local attacker to crash the system or leak kernel internal information. The highest threat from this vulnerability is to system availability.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2021-3739?

It affects 10 products.


Products: Fedoraproject Fedora, Linux kernel, Netapp H300e Firmware, Netapp H300s Firmware, Netapp H410c Firmware, Netapp H410s Firmware, Netapp H500e Firmware, Netapp H500s Firmware, Netapp H700e Firmware, Netapp H700s Firmware.

## How do I fix CVE-2021-3739?

Apply the vendor's patch.

## Is CVE-2021-3739 being exploited?

There is no known exploitation of CVE-2021-3739 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3739 and fix it if it is affected.

What it is: CVE-2021-3739 is a high-severity vulnerability in Fedoraproject Fedora, published on 7 Mar 2022. 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-2021-3739 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. 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-2021-3739/ (Markdown: https://insights.sbomify.com/CVE-2021-3739/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3739
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3739
- OSV: https://osv.dev/vulnerability/CVE-2021-3739

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3739/
Summaries are generated and may contain mistakes; the official description above is the record.