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CVE-2021-3493

7.8, high Known exploited

Linux Kernel Privilege Escalation Vulnerability

NVD (opens in a new tab) CVE.org (opens in a new tab) CISA KEV catalogue (opens in a new tab)
CVSS
7.8, high high CVSS v3.1
EPSS, next 30 days
49% higher than 98.8% of scored CVEs
Exploitation
Confirmed in the wild
Published
17 Apr 20215 years ago

Known exploited

CISA added this to the Known Exploited Vulnerabilities Catalog on 20 Oct 2022. US federal agencies had to remediate by 10 Nov 2022, a deadline that has passed.

Required action. Apply updates per vendor instructions.

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.

Details

Vendor
Linux
Product
linux kernel
Weakness
CWE-270 (opens in a new tab)
Status
Analyzed
Updated
17 Jun 2026
Assigner
security@ubuntu.com

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

References 7

Exploit code 3

Patches and fixes 1

Advisories 2

Other references 1

The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.

Other Linux CVEs

Every Linux CVE we hold

Same vendor in what we hold, not a known link between the flaws.

  • CVE-2026-53362 Linux Kernel Unspecified Vulnerability KEV EPSS 0.7% 7.8, high
  • CVE-2026-53266 Linux Kernel Out-of-Bounds Write Vulnerability KEV EPSS 0.8% 8.8, high
  • CVE-2026-31431 Linux Kernel Incorrect Resource Transfer Between Spheres Vulnerability KEV EPSS 3% 7.8, high
  • CVE-2025-39964 Linux Kernel Race Condition Vulnerability KEV EPSS 1% 5.5, medium
  • CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability KEV EPSS 3% 9.8, critical
  • CVE-2025-38352 Linux Kernel Time-of-Check Time-of-Use (TOCTOU) Race Condition Vulnerability KEV EPSS 1% 7.8, high
  • CVE-2024-53197 Linux Kernel Out-of-Bounds Access Vulnerability KEV EPSS 4% 7.8, high
  • CVE-2024-53150 Linux Kernel Out-of-Bounds Read Vulnerability KEV EPSS 1% 7.1, high

Beyond this page

Is CVE-2021-3493 in your network?

This page tells you how dangerous CVE-2021-3493 is out there. Whether it sits on one of your devices, only a scan of your own network can tell. That is what our systems do, every day, for the companies we protect.

CVE-2021-3493 is in the CISA catalogue of exploited vulnerabilities: attackers are already exploiting it.

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  • EXYS7950 KONDRA

    Detect it if it's exploited

    Until the patch is applied, Kondra monitors your network, events and endpoints in real time. It keeps an inventory of the software installed on every endpoint, and its anomaly detection rules flag what an attacker does once inside.

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Check your exposure

Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 17 Oct 2026, not the live upstream state.