# CVE-2021-47107: NFSD: Fix READDIR buffer overflow

> A buffer overflow in the Linux kernel NFSD READDIR handler allows attackers to write beyond buffer boundaries, potentially causing crashes or code execution.

- **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:** 4 Mar 2024
- **Updated:** 14 Oct 2026
- **Also known as:** DEBIAN-CVE-2021-47107, GHSA-2mfm-m7q3-xch8, UBUNTU-CVE-2021-47107

## What is CVE-2021-47107?

CVE-2021-47107 is a critical vulnerability in Linux kernel, published on 4 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:

NFSD: Fix READDIR buffer overflow

If a client sends a READDIR count argument that is too small (say,
zero), then the buffer size calculation in the new init_dirlist
helper functions results in an underflow, allowing the XDR stream
functions to write beyond the actual buffer.

This calculation has always been suspect. NFSD has never sanity-
checked the READDIR count argument, but the old entry encoders
managed the problem correctly.

With the commits below, entry encoding changed, exposing the
underflow to the pointer arithmetic in xdr_reserve_space().

Modern NFS clients attempt to retrieve as much data as possible
for each READDIR request. Also, we have no unit tests that
exercise the behavior of READDIR at the lower bound of @count
values. Thus this case was missed during testing.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2021-47107?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47107?

Apply the vendor's patch.

## Is CVE-2021-47107 being exploited?

There is no known exploitation of CVE-2021-47107 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-2021-47107 and fix it if it is affected.

What it is: CVE-2021-47107 is a critical vulnerability in Linux kernel, published on 4 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-2021-47107 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-2021-47107/ (Markdown: https://insights.sbomify.com/CVE-2021-47107/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47107
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47107
- OSV: https://osv.dev/vulnerability/CVE-2021-47107

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47107/
Summaries are generated and may contain mistakes; the official description above is the record.