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Fencer Vulns
high 8.8

CVE-2021-3492 json

Ubuntu linux kernel shiftfs file system double free vulnerability

published 2021-04-17 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26814

cvss
8.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.5%
EPSS 1.5% chance of exploitation in 30 days, percentile 75%
public exploits
0
none known

Summary

Shiftfs, an out-of-tree stacking file system included in Ubuntu Linux kernels, did not properly handle faults occurring during copy_from_user() correctly. These could lead to either a double-free situation or memory not being freed at all. An attacker could use this to cause a denial of service (kernel memory exhaustion) or gain privileges via executing arbitrary code. AKA ZDI-CAN-13562.

Patch / fix

  • Ubuntu Linux kernel 5.4.0-72.80, 5.8.0-50.56
  • linux Ubuntu 20.04 LTS 5.4.0-72.80
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1045.47
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1042.45
  • linux-gke Ubuntu 20.04 LTS 5.4.0-1042.44
  • linux-hwe Ubuntu 18.04 LTS 5.3.0-73.69
  • linux-kvm Ubuntu 20.04 LTS 5.4.0-1038.39
  • linux-azure Ubuntu 20.04 LTS 5.4.0-1046.48
  • linux-gkeop Ubuntu 20.04 LTS 5.4.0-1014.15

ubuntu advisories UBUNTU-CVE-2021-3492

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-2021-3492 updated cvss 7.8

kernel: shiftfs file system double free vulnerability

  • 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

Exploit prediction

1.54% chance of exploitation in the next 30 days, higher than 75% of all scored CVEs (FIRST EPSS, 2026-11-08).

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-415 Double Free
  • CWE-401 Missing Release of Memory after Effective Lifetime

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.