# CVE-2021-41091: Insufficiently restricted permissions on data directory in Docker Engine

> Unprivileged Linux users can read, modify, or execute files in Docker data directories due to insufficient permissions, potentially compromising container isolation.

- **Severity:** Medium 6.3 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L`)
- **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:** 4 Oct 2021
- **Updated:** 4 Aug 2024
- **Also known as:** CLEANSTART-2026-OT60529, DEBIAN-CVE-2021-41091, GHSA-3fwx-pjgw-3558, GO-2024-2500, UBUNTU-CVE-2021-41091

## What is CVE-2021-41091?

CVE-2021-41091 is a medium-severity missing authorization vulnerability in Fedoraproject Fedora, published on 4 Oct 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Moby is an open-source project created by Docker to enable software containerization. A bug was found in Moby (Docker Engine) where the data directory (typically `/var/lib/docker`) contained subdirectories with insufficiently restricted permissions, allowing otherwise unprivileged Linux users to traverse directory contents and execute programs. When containers included executable programs with extended permission bits (such as `setuid`), unprivileged Linux users could discover and execute those programs. When the UID of an unprivileged Linux user on the host collided with the file owner or group inside a container, the unprivileged Linux user on the host could discover, read, and modify those files. This bug has been fixed in Moby (Docker Engine) 20.10.9. Users should update to this version as soon as possible. Running containers should be stopped and restarted for the permissions to be fixed. For users unable to upgrade limit access to the host to trusted users. Limit access to host volumes to trusted containers.

Weakness: CWE-732 (Incorrect Permission Assignment for Critical Resource), CWE-281 (Improper Preservation of Permissions)

## Which versions are affected by CVE-2021-41091?

6 open source packages ship an affected version, including github.com/docker/docker and github.com/moby/moby. It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/docker/docker` | Go | All versions | 20.10.9 |
| `github.com/docker/docker` | Go | All versions | 20.10.9 |
| `github.com/docker/docker` | Go | All versions | 20.10.9+incompatible |
| `github.com/moby/moby` | Go | All versions | 20.10.9 |
| `github.com/moby/moby` | Go | All versions | 20.10.9 |
| `github.com/moby/moby` | Go | All versions | 20.10.9+incompatible |

Products: Fedoraproject Fedora, Mobyproject Moby.

## How do I fix CVE-2021-41091?

Upgrade github.com/docker/docker to a fixed version for your release line: 20.10.9 or 20.10.9+incompatible.

## Is CVE-2021-41091 being exploited?

There is no known exploitation of CVE-2021-41091 in the wild and no public exploit code.

Public exploit code:

- POC for CVE-2021-41091 (github_poc): https://github.com/UncleJ4ck/CVE-2021-41091
- This exploit offers an in-depth look at the CVE-2021-41091 security vulnerability and provides a step-by-step guide on how to utilize the exploit script to achieve privilege escalation on a host. (github_poc): https://github.com/SNE-M23-SN/Vulnerable-Docker-Engine
- https://github.com/jrbH4CK/CVE-2021-41091 (github_poc): https://github.com/jrbH4CK/CVE-2021-41091

## 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-2021-41091 and fix it if it is affected.

What it is: CVE-2021-41091 is a medium-severity missing authorization vulnerability in Fedoraproject Fedora, published on 4 Oct 2021. 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-2021-41091 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/docker/docker (Go): affected all versions; fixed in 20.10.9
- github.com/docker/docker (Go): affected all versions; fixed in 20.10.9
- github.com/docker/docker (Go): affected all versions; fixed in 20.10.9+incompatible
- github.com/moby/moby (Go): affected all versions; fixed in 20.10.9
- github.com/moby/moby (Go): affected all versions; fixed in 20.10.9
- github.com/moby/moby (Go): affected all versions; fixed in 20.10.9+incompatible

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-2021-41091/ (Markdown: https://insights.sbomify.com/CVE-2021-41091/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-41091
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-41091
- OSV: https://osv.dev/vulnerability/CVE-2021-41091

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-41091/
Summaries are generated and may contain mistakes; the official description above is the record.