CVE-2021-3493

Name: CVE-2021-3493
Creator: NVD / NIST
Published: 2021-04-17T05:15:14.63+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.8/10Actively ExploitedEPSS 43.99%

Last modified Jun 17, 2026

CVE-2021-3493 is a high-severity vulnerability rated 7.8/10 on the CVSS scale. 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.. CISA has confirmed active exploitation in the wild. EPSS estimates a 43.99% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1

7.8/10

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

43.99%

98.6th percentile

Probability of exploitation in the next 30 days. Learn more

Exploitation Status

This vulnerability is listed in CISA’s Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. Federal agencies must remediate by Nov 10, 2022.

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Canonical	Ubuntu Linux	< 18.04
Canonical	Ubuntu Linux	>= 18.04.1, < 20.04
Canonical	Ubuntu Linux	< 20.10

References

http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.htmlExploit, Third Party Advisory, VDB Entry
http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.htmlPress/Media Coverage, Third Party Advisory, VDB Entry
http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.htmlExploit, Third Party Advisory, VDB Entry
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52Mailing List, Patch, Third Party Advisory
https://ubuntu.com/security/notices/USN-4917-1Vendor Advisory
https://www.openwall.com/lists/oss-security/2021/04/16/1Mailing List, Third Party Advisory
http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.htmlExploit, Third Party Advisory, VDB Entry
http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.htmlPress/Media Coverage, Third Party Advisory, VDB Entry
http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.htmlExploit, Third Party Advisory, VDB Entry
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52Mailing List, Patch, Third Party Advisory
https://ubuntu.com/security/notices/USN-4917-1Vendor Advisory
https://www.openwall.com/lists/oss-security/2021/04/16/1Mailing List, Third Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3493US Government Resource

Timeline

Published: Apr 17, 2021
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2021-3493?

How severe is CVE-2021-3493?

CVE-2021-3493 has a CVSS score of 7.8/10 (HIGH severity). The EPSS model estimates a 43.99% probability of exploitation in the next 30 days. This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog.

How do I fix CVE-2021-3493?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-3493?

Run a free Strix scan to check your systems for this vulnerability.

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Source: NVD / NIST