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.
- 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
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.
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 | 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 include 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.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
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: 3 proofs of concept on GitHub.
Other vulnerabilities in Fedoraproject Fedora
Sources
Also known as CLEANSTART-2026-OT60529, DEBIAN-CVE-2021-41091, GHSA-3fwx-pjgw-3558, GO-2024-2500, UBUNTU-CVE-2021-41091.