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NVD / CVE Program· CNA canonical

CVE-2021-3493: The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities

Noroxi assessment

Priority: This week (action score 76/100)

  • CISA has confirmed exploitation in the wild (Oct 20, 2022). Remediation deadline for US federal agencies: Nov 10, 2022.
  • A ready-made attack module is public (Metasploit); exploiting it takes no special expertise.
  • Probability of exploitation in the next 30 days: 49.1% (FIRST EPSS); higher than 98.8% of all records.
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: linux (Debian:12) 5.10.38-1.

Don’t wait for the next maintenance window. Upgrade to linux (Debian:12) 5.10.38-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · CISA KEV · FIRST EPSS

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.

HighCVSS 7.8 · v3.1KEVWeaponized Fix available
Published
Apr 17, 2021
Updated
Jun 17, 2026
EPSS
49.1% · 98th percentile

Report tools

JSON

Action score

76

This week

Don’t wait for the next maintenance window.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
30 / 30 · Listed
EPSS
15 / 30 · 49.1%

CISA SSVC decision

Exploitation
active
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
7.8
CNA · canonical
8.8
1.0 point gap

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Actively exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on Oct 20, 2022. That signals real attacks, not theory.

Remediation deadline for US federal agencies: Nov 10, 2022.

Get told when this record changes

  • In CISA KEV: exploitation in the wild confirmed
  • Weaponized exploit exists
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-3493

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
canonicalubuntu linux

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • canonical ubuntu linuxbefore 18.04
  • canonical ubuntu linux18.04.1 and later · before 20.04
  • canonical ubuntu linuxbefore 20.10

Versions reported by the vendor

Affected version ranges reported by the assigning authority (canonical). Independent of NVD's CPE analysis and usually ahead of it.

  • Ubuntu linux kernel

    • 5.8 kernel and later · before 5.8.0-50.56affected
    • 5.4 kernel and later · before 5.4.0-72.80affected
    • 4.15 kernel and later · before 4.15.0-142.146affected
    • 4.4 kernel and later · before 4.4.0-209.241affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 5.10.38-15.10.38-1

Same product

canonical: all records

Other highest-scoring records for the same primary product.

  • CVE-2017-14492Heap-based buffer overflow in dnsmasq before 2.78 allows remote attackers to cause a denial of service (crash) or execute arbitrary code via
    67This week
  • CVE-2017-14493Stack-based buffer overflow in dnsmasq before 2.78 allows remote attackers to cause a denial of service (crash) or execute arbitrary code vi
    65This week
  • CVE-2016-4553client_side.cc in Squid before 3.5.18 and 4.x before 4.0.10 does not properly ignore the Host header when absolute-URI is provided, which al
    58Plan

Published before and after this one in the same product

  • ← EarlierCVE-2020-27349Dec 9, 2020 · aptdaemon performed policykit permissions checks too late
    22Monitor
  • ← EarlierCVE-2021-3492Apr 17, 2021 · Ubuntu linux kernel shiftfs file system double free vulnerability
    31Monitor
  • Later →CVE-2021-32547Jun 12, 2021 · apport read_file() function could follow maliciously constructed symbolic links
    22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
debian:linux5.10.38-1 · Debian:12Package registry (OSV)

Exploit status

Weaponized

A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.

Evidence

  • Metasploit module ×1
  • Proof-of-concept repository on GitHub ×21

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Metasploit moduleexploit/linux/local/cve_2021_3493_overlayfs2021 Ubuntu Overlayfs LPEexploit2021-04-12
Proof-of-concept repository on GitHubstars:4452021-04-19
Proof-of-concept repository on GitHubstars:32021-04-22
Proof-of-concept repository on GitHubstars:02021-05-02
Proof-of-concept repository on GitHubstars:422021-07-07
Proof-of-concept repository on GitHubstars:02021-07-16
Proof-of-concept repository on GitHubstars:22021-09-12
Proof-of-concept repository on GitHubstars:22021-10-02
Proof-of-concept repository on GitHubstars:12022-11-29
Proof-of-concept repository on GitHubstars:02023-01-16
Proof-of-concept repository on GitHubstars:02023-08-25
Proof-of-concept repository on GitHubstars:02024-07-04

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Metasploit-5 d
  2. Published
  3. First PoC+2 d
  4. CISA KEV+551 d
  5. TodayNov 2, 2026+2026 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-270 · Privilege Context Switching Error

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (4 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records