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Fencer Vulns
high 8.8

CVE-2021-3493 kev in the critical feed json

The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities…

published 2021-04-17 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26815

cvss
8.8
version 3.1, CNA
cisa kev
Exploited
added 2022-10-20
epss
49.2%
EPSS 49.2% chance of exploitation in 30 days, percentile 98%
public exploits
1
Metasploit

Summary

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.

Patch / fix

cisa required action Apply updates per vendor instructions.

  • Ubuntu linux kernel 4.4.0-209.241, 4.15.0-142.146, 5.4.0-72.80, 5.8.0-50.56
  • linux Debian 14, Debian 13, Debian 12 5.10.38-1

debian advisories DEBIAN-CVE-2021-3493

  • linux Ubuntu 16.04 LTS 4.4.0-209.241
  • linux Ubuntu 18.04 LTS 4.15.0-142.146
  • linux Ubuntu 20.04 LTS 5.4.0-72.80
  • linux-aws Ubuntu 16.04 LTS 4.4.0-1127.141
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1099.106
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1045.47
  • linux-gcp Ubuntu 16.04 LTS 4.15.0-1098.111~16.04.1
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1042.45

ubuntu advisories UBUNTU-CVE-2021-3493

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-3493 updated cvss 7.4

kernel: overlayfs file system caps privilege escalation

  • Red Hat Enterprise Linux 5 kernel Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, kernel-alt, python-perf, +9 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Timeline

  1. First public exploit (Metasploit exploit/linux/local/cve_2021_3493_overlayfs)
  2. Published
  3. Added to CISA KEV
  4. CISA patch deadline
  5. CISA SSVC: exploitation active

Known exploited

Added
4 y ago
Patch by
2022-11-10 (3 y ago)
Ransomware
Not known
Required action
Apply updates per vendor instructions.
Vendor, product
Linux, Kernel
CISA name
Linux Kernel Privilege Escalation Vulnerability

CISA SSVC

Exploitation
Active, exploited in the wild
Automatable
no
Technical impact
total
Assessed
21 mo ago

Exploit prediction

49.17% chance of exploitation in the next 30 days, higher than 98% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

CVSS scores

assigned by version score vector
CNA 3.1 8.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.2 AV:L/AC:L/Au:N/C:C/I:C/A:C

Affected products

  • Ubuntu linux kernel

Classification

Weakness
  • CWE-270 Privilege Context Switching Error
  • CWE-863 Incorrect Authorization

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.