High 8.8Known exploited (CISA KEV)Published Apr 17, 2021

CVE-2021-3493The 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.

Updated under an hour ago (Oct 26, 2026, 11:50 PM ET)

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It affects Ubuntu linux kernel and 1 other product. Add what you run to find out whether that includes you.

CISA lists it as known exploited since Oct 20, 2022; federal agencies had to remediate by Nov 10, 2022. Treat that date as your deadline.

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Exploited in the last 30 days

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.

CVSS: 8.8 HIGH (v3.1, CNA)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Weakness (CWE): CWE-270
Known exploited: Added to CISA KEV Oct 20, 2022; federal remediation due Nov 10, 2022Apply updates per vendor instructions.
EPSS (exploitation in the next 30 days): 49.17% (percentile 99)
Assigned by: canonical
NVD analysis: Analyzed
Record last updated: Oct 21, 2025
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Ubuntu linux kernel ubuntu:linux_kernel (from the name)	from 5.8 kernel before 5.8.0-50.56; from 5.4 kernel before 5.4.0-72.80; from 4.15 kernel before 4.15.0-142.146; from 4.4 kernel before 4.4.0-209.241	CNA record
canonical ubuntu_linux canonical:ubuntu_linux	before 18.04; from 18.04.1 before 20.04; before 20.10	NVD

References

References

https://ubuntu.com/security/notices/USN-4917-1	x-refsource-misc, vendor-advisory
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52	x-refsource-misc, mailing-list, patch, third-party-advisory
https://www.openwall.com/lists/oss-security/2021/04/16/1	x-refsource-misc, mailing-list, third-party-advisory
http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.html	x-refsource-misc, exploit, third-party-advisory, vdb-entry
http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.html	x-refsource-misc, press/media-coverage, third-party-advisory, vdb-entry
http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.html	x-refsource-misc, exploit, third-party-advisory, vdb-entry
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3493	us-government-resource

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.