# CVE-2021-3178: Path traversal in n/a

> Remote attackers can traverse filesystem directories via READDIRPLUS when NFS exports a subdirectory, potentially reading unauthorized files.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jan 2021
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-3178, GHSA-7fjq-g87x-vg8r, UBUNTU-CVE-2021-3178

## What is CVE-2021-3178?

CVE-2021-3178 is a medium-severity path traversal vulnerability in Debian Debian Linux, published on 19 Jan 2021. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

fs/nfsd/nfs3xdr.c in the Linux kernel through 5.10.8, when there is an NFS export of a subdirectory of a filesystem, allows remote attackers to traverse to other parts of the filesystem via READDIRPLUS. NOTE: some parties argue that such a subdirectory export is not intended to prevent this attack; see also the exports(5) no_subtree_check default behavior

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2021-3178?

It affects 3 products.


Products: Debian Debian Linux, Fedoraproject Fedora, Linux kernel.

## How do I fix CVE-2021-3178?

Apply the vendor's patch.

## Is CVE-2021-3178 being exploited?

There is no known exploitation of CVE-2021-3178 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3178 and fix it if it is affected.

What it is: CVE-2021-3178 is a medium-severity path traversal vulnerability in Debian Debian Linux, published on 19 Jan 2021. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-3178 in the wild and no public exploit code.

Affected product: Debian Debian Linux. 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-2021-3178/ (Markdown: https://insights.sbomify.com/CVE-2021-3178/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3178
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3178
- OSV: https://osv.dev/vulnerability/CVE-2021-3178

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3178/
Summaries are generated and may contain mistakes; the official description above is the record.