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CVE-2021-3493

Linux Kernel Privilege Escalation

8.8 HIGHActively exploited (CISA KEV)Public exploitEPSS 49.2%
  1. Published17 Apr 2021
  2. Added to CISA KEV20 Oct 2022
  3. Remediation due10 Nov 2022
Actively exploited (CISA KEV)

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.

Added to KEV: 20 Oct 2022Federal remediation due: 10 Nov 2022

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.

CVSS 3.1 breakdown

Attack vectorLocal
Attack complexityLow
Privileges requiredLow
User interactionNone
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Affected products

Canonical Ubuntu Linux< 20.10 · ≥ 18.04.1 < 20.04 · < 18.04

Remediation

Fixed in
Canonical Ubuntu Linux≥ 20.10

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Frequently asked

Is CVE-2021-3493 being actively exploited?

Yes. CVE-2021-3493 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 20 Oct 2022.

How severe is CVE-2021-3493?

CVE-2021-3493 has a CVSS 3.1 base score of 8.8, rated high. EPSS estimates a 49.2% probability of exploitation.

Which products are affected by CVE-2021-3493?

Affected products include Canonical Ubuntu Linux.

How do I fix CVE-2021-3493?

Upgrade affected software to a fixed version, for example Canonical Ubuntu Linux 20.10 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2021-3493 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, a risk for it never ranks below high, and the update that fixes it moves to the Emergency patch lane. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.