CVE-2021-3493: Linux Kernel Privilege Escalation Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 20 Oct 2022, 551 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 49.2%
EPSS score, percentile 98.9 of all scored records
- How severe?
- 8.8 High
CVSS v3.1 base score, given by the CNA
- What should I do?
Required action (CISA), due 10 Nov 2022: Apply updates per vendor instructions.
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected: 5.8 kernel up to, not including, 5.8.0-50.56; 5.4 kernel up to, not including, 5.4.0-72.80; 4.15 kernel up to, not including, 4.15.0-142.146; 4.4 kernel up to, not including, 4.4.0-209.241
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
What to do
Required action, set by CISA
Apply updates per vendor instructions.
CISA due date for this action: 10 November 2022.
Solution (from the CVE record)
Apply https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52
Workaround (from the CVE record)
Disable unprivileged user namespaces.
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
Linked from CISA's catalog entry
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52
- https://nvd.nist.gov/vuln/detail/CVE-2021-3493
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | 5.8 kernel up to, not including, 5.8.0-50.56 |
| Affected | 5.4 kernel up to, not including, 5.4.0-72.80 |
| Affected | 4.15 kernel up to, not including, 4.15.0-142.146 |
| Affected | 4.4 kernel up to, not including, 4.4.0-209.241 |
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
About this vulnerability
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.
Summary: CISA's KEV catalog, as of 28 Oct 2026.
- CISA added CVE-2021-3493 to its Known Exploited Vulnerabilities (KEV) catalog on 20 Oct 2022.
- CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
- The due date CISA sets for the required action is 10 Nov 2022.
- The CVE record was published on 17 Apr 2021, 551 days before it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 8.8 (High), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 49.2% (percentile 98.9), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact total.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.
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.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
Weakness
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| 17 Apr 2021 | CVE record published |
| 20 Oct 2022 | Added to CISA KEV |
| 10 Nov 2022 | CISA due date for the required action |
| 21 Oct 2025 | CVE record last updated |
References
- ubuntu.com
- git.kernel.org
- openwall.com
- packetstormsecurity.com
- packetstormsecurity.com
- packetstormsecurity.com
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