CVE-2021-41091

MEDIUM

Moby < 20.10.9 - Unprivileged Host User Data Exposure and Privilege Escalation via Insufficient Directory Permissions

Title source: llm
STIX 2.1

Exploitation Summary

EIP tracks 4 public exploits for CVE-2021-41091. PoCs published by UncleJ4ck, SNE-M23-SN, JorgeRh4ck.

AI-analyzed exploit summary This repository contains a working exploit for CVE-2021-41091, a privilege escalation vulnerability in Moby (Docker Engine) due to improperly restricted permissions in /var/lib/docker/overlay2. The exploit script checks for vulnerable Docker versions and attempts to spawn a root shell by leveraging setuid binaries in container filesystems.

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.

Exploits (4)

nomisec WORKING POC 65 stars
by UncleJ4ck · poc
https://github.com/UncleJ4ck/CVE-2021-41091

This repository contains a working exploit for CVE-2021-41091, a privilege escalation vulnerability in Moby (Docker Engine) due to improperly restricted permissions in /var/lib/docker/overlay2. The exploit script checks for vulnerable Docker versions and attempts to spawn a root shell by leveraging setuid binaries in container filesystems.

Classification
Working Poc 95%
Attack Type
Lpe
Complexity
Moderate
Reliability
Reliable
Target: Moby (Docker Engine) < 20.10.9
No auth needed
Prerequisites: Unprivileged access to a host with vulnerable Docker Engine · A running Docker container with writable access to modify /bin/bash permissions
devstral-2 · analyzed Feb 16, 2026 Full analysis →
nomisec WORKING POC 2 stars
by SNE-M23-SN · poc
https://github.com/SNE-M23-SN/Vulnerable-Docker-Engine

This PoC exploits CVE-2021-41091, a Docker Engine vulnerability allowing unprivileged users to traverse and execute setuid programs in the Docker data directory. The exploit script checks for vulnerable Docker versions, iterates over overlay2 filesystems, and spawns a root shell if a setuid binary is found.

Classification
Working Poc 95%
Attack Type
Lpe
Complexity
Moderate
Reliability
Reliable
Target: Docker Engine (Moby) versions < 20.10.9
No auth needed
Prerequisites: Docker Engine < 20.10.9 · Access to a container with root privileges to set setuid on /bin/bash · Unprivileged user access on the host
devstral-2 · analyzed Feb 16, 2026 Full analysis →
github WORKING POC 1 stars
by JorgeRh4ck · pythonpoc
https://github.com/JorgeRh4ck/CVE-Exploits/tree/main/CVE-2021-41091

This repository contains a functional exploit for CVE-2021-41091, a directory traversal vulnerability in Moby (Docker Engine) that allows unprivileged users to execute programs on the host machine with elevated privileges. The exploit involves running scripts inside a container and on the host to achieve privilege escalation via a SUID binary.

Classification
Working Poc 90%
Attack Type
Lpe
Complexity
Moderate
Reliability
Reliable
Target: Moby (Docker Engine) 20.10.5+dfsg1
No auth needed
Prerequisites: Docker container with root access to execute docker.sh · Host machine running vulnerable Moby version
devstral-2 · analyzed Feb 27, 2026 Full analysis →
nomisec WORKING POC
by jrbH4CK · poc
https://github.com/jrbH4CK/CVE-2021-41091

This PoC exploits CVE-2021-41091, a directory traversal vulnerability in Moby (Docker Engine), allowing unprivileged users to execute programs from the container on the host machine with elevated privileges. The exploit involves setting the SUID bit on /bin/bash within the container and leveraging directory traversal to execute it on the host.

Classification
Working Poc 90%
Attack Type
Lpe
Complexity
Moderate
Reliability
Reliable
Target: Moby (Docker Engine) 20.10.5+dfsg1
No auth needed
Prerequisites: Access to a container with the ability to run scripts as root · Host running a vulnerable version of Moby (Docker Engine)
devstral-2 · analyzed Feb 16, 2026 Full analysis →

Scores

CVSS v3 6.3
EPSS 0.0475
EPSS Percentile 89.7%
Attack Vector LOCAL
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L

Details

CWE
CWE-281 CWE-732
Status published
Products (5)
docker/docker 0 - 20.10.9Go
fedoraproject/fedora 34
fedoraproject/fedora 35
moby/moby 0 - 20.10.9Go
mobyproject/moby < 20.10.9
Published Oct 04, 2021
Tracked Since Feb 18, 2026