CVE-2021-3493

Privilege Context Switching Error

CVSS 3.1 High 8.8Known exploited (CISA KEV)

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

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.

Key data

CVSS 3.1 High 8.8

Score published by canonical in the CVE record.

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

Attack vector: Local
The attacker needs local access to the system, or to trick a user into running something.
Attack complexity: Low
No special conditions are needed. The attack can be repeated at will.
Privileges required: Low
A basic user account is needed.
User interaction: None
No action from any user is needed.
Scope: Changed
The impact can reach other components beyond the vulnerable one.
Confidentiality impact: High
Serious or total effect on the secrecy of data.
Integrity impact: High
Serious or total effect on the trustworthiness of data.
Availability impact: High
Serious or total effect on availability.

Metric	Value	What it means
Attack vector	Local	The attacker needs local access to the system, or to trick a user into running something.
Attack complexity	Low	No special conditions are needed. The attack can be repeated at will.
Privileges required	Low	A basic user account is needed.
User interaction	None	No action from any user is needed.
Scope	Changed	The impact can reach other components beyond the vulnerable one.
Confidentiality impact	High	Serious or total effect on the secrecy of data.
Integrity impact	High	Serious or total effect on the trustworthiness of data.
Availability impact	High	Serious or total effect on availability.

CVSS is owned and managed by FIRST.Org, Inc. (FIRST) and is used by permission. Each CVSS score on this site is shown together with its vector string, as published in the CVE record by the source named next to it. Learn more at first.org/cvss.

EPSS

Exploit Prediction Scoring System by FIRST: an estimate of the probability that exploitation activity will be observed in the next 30 days.

Score: 0.49166 (49.2% probability)
Percentile: 98.9%
Scores of: Nov 10, 2026
Model: v2026.06.15

CISA Known Exploited Vulnerabilities

This CVE is listed in the CISA KEV catalog.

Name in the catalog: Linux Kernel Privilege Escalation Vulnerability
Added to the catalog: Oct 20, 2022
Federal due date: Nov 10, 2022

CISA assessment as of Feb 7, 2025

Stakeholder-Specific Vulnerability Categorization (SSVC) decision points added by CISA.

Exploitation: Recorded by CISA as active
Automatable: no
Technical impact: total

Weakness (CWE)

CWE catalog version 5.0.

CWE-270Privilege Context Switching Error

Affected products

Products listed in the CVE record, as the CNA published them.

Ubuntu linux kernel
- affected: 5.8 kernel up to before 5.8.0-50.56
- affected: 5.4 kernel up to before 5.4.0-72.80
- affected: 4.15 kernel up to before 4.15.0-142.146
- affected: 4.4 kernel up to before 4.4.0-209.241

References

Links listed in the CVE record. They lead to other sites, which CubePath does not control.

Timeline

ID reservedApr 12, 2021
Record publishedApr 17, 2021
Added to CISA KEVOct 20, 2022
Record last updatedOct 21, 2025

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Data from the CVE Program (MITRE), CISA KEV and FIRST EPSS. CVSS is owned by FIRST and used by permission. Not affiliated with or endorsed by MITRE, CISA or FIRST. Data as of Nov 10, 2026, 19:51 UTC. Sources and licenses