How severe is CVE-2021-3493?

CVE-2021-3493 has a CVSS score of 7.8/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-3493?

Affected package information for CVE-2021-3493 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-3493?

No fixed release is recorded for CVE-2021-3493 yet. Track the upstream advisory, and apply the exposure-reduction steps below in the meantime.

How do I detect CVE-2021-3493 in my code and dependencies?

Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).

How do I mitigate CVE-2021-3493 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2021-3493 actively exploited in the wild?

Yes. There are 12 known exploit references for CVE-2021-3493, including 9 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-3493?

CVE-2021-3493 has an EPSS (Exploit Prediction Scoring System) score of 49.2%, placing it in the 99th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score warrants monitoring and prompt remediation.

Is CVE-2021-3493 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-3493 (Linux Kernel Privilege Escalation Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2022-10-20. CISA required all US federal civilian agencies to remediate this vulnerability by 2022-11-10. The required action was: Apply updates per vendor instructions. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2021-3493?

CVE-2021-3493 is classified as CWE-270 (CWE-270), CWE-863 (CWE-863). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-3493 published, and has it been updated?

CVE-2021-3493 was published on April 17, 2021 and was last updated on March 15, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🛡️

CISA KEV · ACTIVELY EXPLOITED

HIGH severity

CVE-2021-3493 — Linux kernel

HIGH

CVE-2021-3493 is a high-severity (CVSS 7.8) CWE-270 vulnerability. It is in CISA's Known Exploited Vulnerabilities catalog (added 2022-10-20) — treat it as actively exploited and patch now. No vendor fix is recorded yet; mitigation options are listed below.

Published

Apr 17, 2021

Updated

Mar 15, 2026

Affected

1 product

Patched

See advisory

Exploits

12 known

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, CISA KEV, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2022-10-20. Federal agencies were required to remediate by 2022-11-10.
A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2021-3493.

EPSS Exploitation Probability

via FIRST.org ↗

49.2%probability of exploitation in next 30 days

High Risk0.00%

Lower risk than most CVEs99th percentile — riskier than 99% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-3493 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,249 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Counts from FIRST.org, log-scaled.

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.

Affected Products

1 product · 3 configurations

ubuntu linuxcanonical

≥ 18.04.1 && < 20.10

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.