The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities on files in an underlying file system. Due to the combination of unprivileged user namespaces along with a patch carried in the Ubuntu kernel to allow unprivileged overlay mounts, an attacker could use this to gain elevated privileges.
Advisories
Source ID Title
Ubuntu USN Ubuntu USN USN-4915-1 Linux kernel (OEM) vulnerabilities
Ubuntu USN Ubuntu USN USN-4916-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-4917-1 Linux kernel vulnerabilities
Fixes

Solution

Apply https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52


Workaround

Disable unprivileged user namespaces.

History

Wed, 22 Oct 2025 00:30:00 +0000


Tue, 21 Oct 2025 20:30:00 +0000


Tue, 21 Oct 2025 19:30:00 +0000


Fri, 07 Feb 2025 13:15:00 +0000

Type Values Removed Values Added
Metrics kev

{'dateAdded': '2022-10-20'}

ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'active', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Wed, 14 Aug 2024 00:45:00 +0000

Type Values Removed Values Added
References

cve-icon MITRE

Status: PUBLISHED

Assigner: canonical

Published:

Updated: 2025-10-21T23:25:48.908Z

Reserved: 2021-04-12T00:00:00.000Z

Link: CVE-2021-3493

cve-icon Vulnrichment

Updated: 2024-08-03T16:53:17.827Z

cve-icon NVD

Status : Analyzed

Published: 2021-04-17T05:15:14.630

Modified: 2025-10-28T13:49:50.883

Link: CVE-2021-3493

cve-icon Redhat

Severity : Moderate

Publid Date: 2021-04-16T00:00:00Z

Links: CVE-2021-3493 - Bugzilla

cve-icon OpenCVE Enrichment

No data.