# CVE-2021-3995: Missing authorization in util-linux

> An unprivileged local attacker can unmount FUSE filesystems belonging to other users, causing denial of service to applications using those filesystems.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/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:** 23 Aug 2022
- **Updated:** 3 Aug 2024
- **Also known as:** ALPINE-CVE-2021-3995, CLEANSTART-2026-WY70417, DEBIAN-CVE-2021-3995, JLSEC-2025-192, UBUNTU-CVE-2021-3995

## What is CVE-2021-3995?

CVE-2021-3995 is a medium-severity missing authorization vulnerability in Fedoraproject Fedora, published on 23 Aug 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A logic error was found in the libmount library of util-linux in the function that allows an unprivileged user to unmount a FUSE filesystem. This flaw allows an unprivileged local attacker to unmount FUSE filesystems that belong to certain other users who have a UID that is a prefix of the UID of the attacker in its string form. An attacker may use this flaw to cause a denial of service to applications that use the affected filesystems.

Weakness: CWE-552 (Files or Directories Accessible to External Parties)

## Which versions are affected by CVE-2021-3995?

It affects 2 products.


Products: Fedoraproject Fedora, Kernel Util-Linux.

## How do I fix CVE-2021-3995?

Apply the vendor's patch.

## Is CVE-2021-3995 being exploited?

There is no known exploitation of CVE-2021-3995 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-2021-3995 and fix it if it is affected.

What it is: CVE-2021-3995 is a medium-severity missing authorization vulnerability in Fedoraproject Fedora, published on 23 Aug 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-2021-3995 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-2021-3995/ (Markdown: https://insights.sbomify.com/CVE-2021-3995/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3995
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3995
- OSV: https://osv.dev/vulnerability/CVE-2021-3995

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3995/
Summaries are generated and may contain mistakes; the official description above is the record.