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Public proof of conceptFix available

CVE-2021-41091

A public proof of concept exists; no exploitation attested.

  • Published2021-10-04
  • WeaknessCWE-281 · CWE-732

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2021-10-0421:15CVE publishedNVD
  2. 2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-41091?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-41091?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD · OSV
Fedoraproject fedora
BranchAffectedFixed in
34.x= 34no fix published
35.x= 35no fix published
Mobyproject moby
BranchAffectedFixed in
20.10< 20.10.920.10.9
20.10< 20.10.9+incompatible20.10.9+incompatible

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • RHSA-2022:0735 Red Hat Product Security221 products fixed

    Red Hat Security Advisory: Red Hat Advanced Cluster Management 2.4.2 security updates and bug fixes

Full record on NVD

Fix

  1. Vendor fix Red Hat Product Security RHSA-2022:0735 · 221 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/documentation/en-us/red_hat_advanced_cluster_management_for_kubernetes/2.4/html-single/install/index#instal…

Advisories and patches

Detection

read 2026-10-23 19:23 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
3 repositories, unverifiedUncleJ4ck/CVE-2021-41091jrbH4CK/CVE-2021-41091SNE-M23-SN/Vulnerable-Docker-Engine
PoC-in-GitHub

Sources

  • CNACVSS 3.16.3read 2026-10-23
  • NVDCVSS 3.16.3read 2026-10-23
  • NVDCVSS 2.04.6read 2026-10-23
  • CNAweakness (CWE)CWE-281read 2026-10-23
  • NVDweakness (CWE)CWE-732read 2026-10-23
  • FIRST EPSSEPSS score2.8 %2026-10-23
  • PoC-in-GitHubproof of concept3read 2026-10-23
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L
Published
2021-10-04
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is CVE-2021-41091?

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.

Is CVE-2021-41091 actively exploited?

Active exploitation of CVE-2021-41091 has not been confirmed. Its EPSS score was 2.8% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-41091?

CVE-2021-41091 has a CVSS v3 base score of 6.3 (MEDIUM severity), with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:L.

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