CVE-2021-3493 (GCVE-0-2021-3493)

Vulnerability from cvelistv5 – Published: 2021-04-17 04:20 – Updated: 2025-10-21 23:25
VLAI CISA KEVIntel
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.
Severity
8.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
SSVC
Exploitation: active Automatable: no Technical Impact: total
CISA Coordinator (v2.0.3)
CWE
  • CWE-270 - Privilege Context Switching Error
Assigner
References
Impacted products
Vendor Product Version
Ubuntu linux kernel Affected: 5.8 kernel , < 5.8.0-50.56 (custom)
Affected: 5.4 kernel , < 5.4.0-72.80 (custom)
Affected: 4.15 kernel , < 4.15.0-142.146 (custom)
Affected: 4.4 kernel , < 4.4.0-209.241 (custom)
Create a notification for this product.
Date Public
2021-04-15 00:00
Credits
An independent security researcher reporting to the SSD Secure Disclosure program
CISA
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: 576f2de9-0f36-4247-b1dd-51b66a575fa5

Vulnerability ID: CVE-2021-3493

Status: Confirmed

Status Updated: 2022-10-20 00:00 UTC

Exploited: Yes

Timestamps
First Seen: 2022-10-20
Asserted: 2022-10-20
Scope
Notes: KEV entry: Linux Kernel Privilege Escalation Vulnerability | Affected: Linux / Kernel | Description: The overlayfs stacking file system in Linux kernel does not properly validate the application of file capabilities against user namespaces, which could lead to privilege escalation. | Required action: Apply updates per vendor instructions. | Due date: 2022-11-10 | Known ransomware campaign use (KEV): Unknown | Notes (KEV): https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52; https://nvd.nist.gov/vuln/detail/CVE-2021-3493
Evidence

Type: Vendor Report

Signal: Successful Exploitation

Confidence: 80%

Source: cisa-kev

Details
Cwes CWE-862
Feed CISA Known Exploited Vulnerabilities Catalog
Product Kernel
Due Date 2022-11-10
Date Added 2022-10-20
Vendorproject Linux
Vulnerabilityname Linux Kernel Privilege Escalation Vulnerability
Knownransomwarecampaignuse Unknown
References
Created: 2026-02-02 13:25 UTC | Updated: 2026-02-06 07:53 UTC
KEVIntel
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: ea54b633-29cb-4291-802a-3a3d3631d6e3

Vulnerability ID: CVE-2021-3493

Status: Confirmed

Status Updated: 2022-10-20 00:00 UTC

Exploited: Yes

Timestamps
First Seen: 2022-10-20
Asserted: 2022-10-20
Scope
Notes: KEVIntel entry: The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities on... | Affected: Ubuntu / linux kernel | CVSS: 8.8 (HIGH) | Used in malware: unknown | Not yet in CISA KEV: False
Evidence

Type: Public Report

Signal: Successful Exploitation

Confidence: 70%

Source: kevintel

Details
Feed KEVIntel (kevintel.com)
Title The overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities on...
Vendor Ubuntu
Product linux kernel
Added Date 2022-10-20T00:00:00.000Z
Cvss Score 8.8
Epss Score None
Cvss Severity HIGH
Epss Percentile None
Used In Malware unknown
Ahead Of Cisa Kev None
Not Yet In Cisa Kev False
References
Created: 2026-06-23 11:14 UTC | Updated: 2026-06-23 11:14 UTC
Show details on NVD website
To clipboard 

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Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.