CVE-2021-3493
HighExploitedPublic exploitThe 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.
Published Apr 17, 2021 · Updated Sep 9, 2026 · Also known as DEBIAN-CVE-2021-3493
Key Facts
Patch immediately- CVE-2021-3493 is a high-severity vulnerability (CVSS 7.8 v3.1) affecting Ubuntu Linux (Canonical), linux (debian), rootio-linux and 22 more products.
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Oct 20, 2022. Public exploit code is available.
- EPSS estimates a 49% probability of exploitation in the next 30 days.
- Fixed versions are available, including Ubuntu Linux 18.04, Ubuntu Linux 20.10, linux 4.15.0-142.146.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
7.8
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
49%
Higher than 98.8% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2021-3493 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
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.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Oct 20, 2022 | Nov 10, 2022 | Not reported |
| Industry KEV feed | Oct 20, 2022 | Nov 10, 2022 | Not reported |
| CIRCL KEV | Oct 20, 2022 | Nov 10, 2022 | Not reported |
| ENISA EUVD | Oct 20, 2022 | n/a | Not reported |
Required action: Apply updates per vendor instructions.
Affected Products
98 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| Ubuntu LinuxCanonical | See advisory | 20.10 |
| linuxdebian | See advisory | 5.10.38-1 |
| rootio-linuxrootio | See advisory | 5.10.38-1 |
| linux-aws-5.0ubuntu | See advisory | n/a |
| linux-aws-5.3ubuntu | See advisory | n/a |
Patched Releases
Ubuntu Linux
18.04, 20.10
linux
4.15.0-142.146, 4.4.0-209.241, 5.10.38-1, 5.4.0-72.80
linux kernel
4.15.0-142.146, 4.4.0-209.241, 5.4.0-72.80, 5.8.0-50.56
linux-aws
4.15.0-1099.106, 4.4.0-1091.95, 4.4.0-1127.141, 5.4.0-1045.47
linux-aws-5.4
5.4.0-1045.47~18.04.1
linux-aws-fips
4.15.0-2042.44, 5.4.0-1069.73+fips2
linux-aws-hwe
4.15.0-1099.106~16.04.1
linux-azure
4.15.0-1113.126~14.04.1, 4.15.0-1113.126~16.04.1, 5.4.0-1046.48
linux-azure-4.15
4.15.0-1113.126
linux-azure-5.4
5.4.0-1046.48~18.04.1
linux-azure-fips
4.15.0-2025.28, 5.4.0-1073.76+fips1
linux-dell300x
4.15.0-1017.21
linux-fips
4.15.0-1058.66, 4.4.0-1061.67
linux-gcp
4.15.0-1098.111~16.04.1, 5.4.0-1042.45
linux-gcp-4.15
4.15.0-1098.111
linux-gcp-5.4
5.4.0-1042.45~18.04.1
linux-gcp-fips
5.4.0-1067.71~20.04.1
linux-gke
5.4.0-1042.44
linux-gke-5.3
5.3.0-1042.45
linux-gke-5.4
5.4.0-1042.44~18.04.1
linux-gkeop
5.4.0-1014.15
linux-gkeop-5.4
5.4.0-1014.15~18.04.1
linux-hwe
4.15.0-142.146~16.04.1, 5.3.0-73.69
linux-hwe-5.4
5.4.0-72.80~18.04.1
linux-hwe-5.8
5.8.0-50.56~20.04.1
Timeline
Publicly disclosed
Apr 17, 2021
Added to CISA KEV
Oct 20, 2022
Added to Industry KEV feed
Oct 20, 2022
Added to CIRCL KEV
Oct 20, 2022
Added to ENISA EUVD
Oct 20, 2022
Last updated
Sep 9, 2026
Weakness Type
- CWE-270 Privilege Context Switching Error
- CWE-552 Files or Directories Accessible to External Parties
- CWE-863 Incorrect Authorization
References
- advisoryhttp://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.html
- advisoryhttps://security-tracker.debian.org/tracker/CVE-2021-3493
- advisoryhttps://ubuntu.com/security/CVE-2021-29154
- advisoryhttps://ubuntu.com/security/CVE-2021-3492
- advisoryhttps://ubuntu.com/security/CVE-2021-3493
FAQ
Common Questions.
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.
Affected: Ubuntu Linux (Canonical); linux (debian); rootio-linux, among others. The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Oct 20, 2022.
Yes. It was added on Oct 20, 2022 with a federal remediation due date of Nov 10, 2022.
Public exploit code is available.
Fixed versions are available, including Ubuntu Linux 18.04, Ubuntu Linux 20.10, linux 4.15.0-142.146.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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