CVE-2021-3493

CVE-2021-3493 is a high-severity vulnerability in Canonical Ubuntu Linux with a CVSS 3.x base score of 8.8. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2022-10-20). The underlying weakness is classified as CWE-863.

Key facts

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.

Frequently asked questions

What is CVE-2021-3493?
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.
How severe is CVE-2021-3493?
CVE-2021-3493 has a CVSS 3.x base score of 8.8, rated high severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-3493 being actively exploited?
Yes. CVE-2021-3493 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2022-10-20, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2021-3493?
CVE-2021-3493 primarily affects Canonical Ubuntu Linux. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-3493?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2021-3493 have an EU (EUVD) identifier?
Yes. CVE-2021-3493 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2021-26815. It is also flagged as exploited in the EUVD (since 2022-10-20).
When was CVE-2021-3493 published?
CVE-2021-3493 was published on 2021-04-17 and last updated on 2026-06-17.

References

Affected products (2)

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