CASCACascade Atlas

Evidence dossier

CVE-2021-3493

CVE-2021-3493

71.3–90.3Priority evidence range
As known Jul 19, 2026, 5:00 AM UTCgen-56ccdaf9

Normalized restatement

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.

State
PUBLISHED
Published
Apr 17, 2021
Updated
Oct 21, 2025
Evidence coverage
72%
CISA KEVCatalog member

Apply updates per vendor instructions.

FIRST EPSS43.99%

2026-07-18 · v2026.06.15 · percentile 98.6%

Source stateConflict visible

Distinct CVSS assessments remain side by side; none are averaged.

Source comparison

Who said what

canonicaloriginal assertion
container

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-ADPindependent enrichment
container

CISA ADP Vulnrichment

CVEderivative copy
container

CVE Program Container

CISA KEVoriginal assertion
observed_exploitation

Linux Kernel Privilege Escalation Vulnerability

FIRST EPSSoriginal assertion
model_probability

Probability 0.439880000000; percentile 0.986100000000

Applicability

Cited product scope

Trace impact →
Ubuntulinux kernel
[{"status": "affected", "version": "5.8 kernel", "lessThan": "5.8.0-50.56", "versionType": "custom"}, {"status": "affected", "version": "5.4 kernel", "lessThan": "5.4.0-72.80", "versionType": "custom"}, {"status": "affected", "version": "4.15 kernel", "lessThan": "4.15.0-142.146", "versionType": "custom"}, {"status": "affected", "version": "4.4 kernel", "lessThan": "4.4.0-209.241", "versionType": "custom"}]unknown
Unknown vendorUnknown product
cpe:2.3:o:canonical:ubuntu_linux:*:*:*:*:-:*:*:*; end excluding 20.10supported
Unknown vendorUnknown product
cpe:2.3:o:canonical:ubuntu_linux:*:*:*:*:lts:*:*:*; end excluding 18.04supported
Unknown vendorUnknown product
cpe:2.3:o:canonical:ubuntu_linux:*:*:*:*:lts:*:*:*; start including 18.04.1; end excluding 20.04supported

Assessments

CVSS by origin

7.8
nvd@nist.govCVSS 3.1 · role PrimaryCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.2
nvd@nist.govCVSS 2.0 · role PrimaryAV:L/AC:L/Au:N/C:C/I:C/A:C
8.8
security@ubuntu.comCVSS 3.1 · role SecondaryCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
8.8
canonicalCVSS 3.1 · role unknownCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Limitations and unknowns

  • KEV membership is authoritative for the catalog, not proof of exposure in any environment.
  • EPSS is a dated model probability and not an individual-environment prediction.
  • Affected or fixed status applies only to the exact cited product and version scope; unresolved scope remains unknown.
  • NVD-carried upstream facts remain derivative and are not independent corroboration.
  • Only NVD metrics validated under the generation-bound calculator are Public Priority eligible; direct CVE record metrics remain display-only.
  • NVD CVSS source eligibility is closed: NVD-authored, exact record-source, or registered same-CVE container origin; unmapped sources remain display-only.
  • Factor D is unknown in Public Core because no accepted canonical mapping-obligation ledger is present.
  • Core replay supports the active and immediately prior generation; retrospective valid-at replay is deferred.