# CVE-2021-47316: nfsd: fix NULL dereference in nfs3svc_encode_getaclres

> A NULL pointer dereference in the Linux kernel NFS server can cause a denial of service when handling specific error cases in ACL encoding.

- **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:** No
- **Published:** 21 May 2024
- **Updated:** 14 Oct 2026
- **Also known as:** GHSA-x95x-w6hq-mwxc, UBUNTU-CVE-2021-47316

## What is CVE-2021-47316?

CVE-2021-47316 is a high-severity vulnerability in Linux kernel, published on 21 May 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:

nfsd: fix NULL dereference in nfs3svc_encode_getaclres

In error cases the dentry may be NULL.

Before 20798dfe249a, the encoder also checked dentry and
d_really_is_positive(dentry), but that looks like overkill to me--zero
status should be enough to guarantee a positive dentry.

This isn't the first time we've seen an error-case NULL dereference
hidden in the initialization of a local variable in an xdr encoder.  But
I went back through the other recent rewrites and didn't spot any
similar bugs.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2021-47316?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47316?

No fix has been published for CVE-2021-47316 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-47316 being exploited?

There is no known exploitation of CVE-2021-47316 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-2021-47316 and fix it if it is affected.

What it is: CVE-2021-47316 is a high-severity vulnerability in Linux kernel, published on 21 May 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-2021-47316 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-2021-47316/ (Markdown: https://insights.sbomify.com/CVE-2021-47316/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47316
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47316
- OSV: https://osv.dev/vulnerability/CVE-2021-47316

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47316/
Summaries are generated and may contain mistakes; the official description above is the record.