# CVE-2021-47179: NFSv4: Fix a NULL pointer dereference in pnfs_mark_matching_lsegs_return()

> A NULL pointer dereference in the Linux kernel's NFSv4 implementation allows local attackers to cause a system crash via specific NFS operations.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 25 Mar 2024
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2021-47179, GHSA-w5g2-4rxc-h7x8, UBUNTU-CVE-2021-47179

## What is CVE-2021-47179?

CVE-2021-47179 is a high-severity vulnerability in Linux kernel, published on 25 Mar 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

NFSv4: Fix a NULL pointer dereference in pnfs_mark_matching_lsegs_return()

Commit de144ff4234f changes _pnfs_return_layout() to call
pnfs_mark_matching_lsegs_return() passing NULL as the struct
pnfs_layout_range argument. Unfortunately,
pnfs_mark_matching_lsegs_return() doesn't check if we have a value here
before dereferencing it, causing an oops.

I'm able to hit this crash consistently when running connectathon basic
tests on NFS v4.1/v4.2 against Ontap.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2021-47179?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47179?

Apply the vendor's patch.

## Is CVE-2021-47179 being exploited?

There is no known exploitation of CVE-2021-47179 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-2021-47179 and fix it if it is affected.

What it is: CVE-2021-47179 is a high-severity vulnerability in Linux kernel, published on 25 Mar 2024. 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-2021-47179 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-2021-47179/ (Markdown: https://insights.sbomify.com/CVE-2021-47179/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47179
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47179
- OSV: https://osv.dev/vulnerability/CVE-2021-47179

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47179/
Summaries are generated and may contain mistakes; the official description above is the record.