CVE-2021-3493
Confirmed PUBLISHEDThe overlayfs implementation in the linux kernel did not properly validate with respect to user namespaces the setting of file capabilities on...
Recommended Action
Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.
At a Glance
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.
- CVE Published
- Apr 17, 2021
- Exploitation Reported
- Oct 20, 2022
- CVSS
- 8.8 High
- EPSS
- —
Affected Versions
| Vendor | Product | Version | Status |
|---|---|---|---|
| Ubuntu |
linux kernel
|
5.8 kernel to < 5.8.0-50.56 |
Affected |
| Ubuntu |
linux kernel
|
5.4 kernel to < 5.4.0-72.80 |
Affected |
| Ubuntu |
linux kernel
|
4.15 kernel to < 4.15.0-142.146 |
Affected |
| Ubuntu |
linux kernel
|
4.4 kernel to < 4.4.0-209.241 |
Affected |
CVE References
- ubuntu.com/security/notices/USN-4917-1 ubuntu.com · CVE Record https://ubuntu.com/security/notices/USN-4917-1
- git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/... git.kernel.org · CVE Record https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co...
- OSS-Security Mailing List openwall.com · CVE Record https://www.openwall.com/lists/oss-security/2021/04/16/1
- packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Noti... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Securit...
- packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privileg... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Pr...
Show 1 more reference
- packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privileg... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Pr...
Recommended Actions
- Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.
- Check enrichment artifacts for scanner coverage and available PoCs before rolling remediation validation.
- Use the Pro API to automate enrichment, telemetry, and workflow delivery for VM, SOC, and CTI pipelines.
Known Exploited Vulnerability Sources
Catalogues that list this CVE as a known exploited vulnerability.
Per-source evidence links for KEV attestations are available through the KEVIntel Pro API.
Learn about Pro API access| Source | Added |
|---|---|
| CISA First | 2022-10-20 00:00 UTC |
Scanner Artifacts
Nuclei and Metasploit references linked to this CVE.
| Scanner | Reference | Detected |
|---|---|---|
| Metasploit | https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/linux/local/cve_2021_3493_overlayfs.rb | Apr 28, 2025 |
Virtual Patch
Compensating WAF rules to help reduce exposure to this CVE. Rule content and deployable vendor exports are available with KEVIntel Enterprise.
KEVIntel does not currently have a virtual patch for this CVE. When available, KEVIntel virtual patches ship as deployable ModSecurity, Cloudflare, and AWS WAF rules.
Enterprise feature. Virtual patch rule content and deployable vendor exports (ModSecurity, Cloudflare, AWS WAF) are available to KEVIntel Enterprise users.
CVSS Scores
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Exploitation Status
Exploited in the wild
Recorded 2022-10-20 00:00:00 UTC · CISA
Proof of concept available
Recorded 2021-04-19 20:07:01 UTC · GitHub
Weaknesses (CWE)
-
Privilege Context Switching Error
Scanner Integrations
| Scanner | Reference | Detected |
|---|---|---|
| Metasploit | https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/linux/local/cve_2021_3493_overlayfs.rb | Apr 28, 2025 |
Potential Proof of Concepts
These PoCs are unverified and could contain malware. Use at your own risk.
github · Created 2024-07-04 17:29:28 UTC · 0 stars
github · Created 2021-10-02 14:44:43 UTC · 0 stars
github · Created 2021-07-07 06:16:48 UTC · 39 stars
CVE-2021-3493 Ubuntu OverlayFS Local Privesc (Interactive Bash Shell & Execute Command Entered)
github · Created 2021-04-22 02:06:21 UTC · 3 stars
github · Created 2021-04-19 20:07:01 UTC · 418 stars
Ubuntu OverlayFS Local Privesc
Timeline
Key exploitation, disclosure, scanner coverage, and KEV attestation events for this CVE.
-
15:02 UTC about 1 year ago15:02 UTC · about 1 year ago
Metasploit module available
Exploit module available
-
00:00 UTC almost 4 years ago00:00 UTC · almost 4 years ago
Added to CISA KEV
Listed in the CISA Known Exploited Vulnerabilities catalog
-
20:07 UTC over 5 years ago20:07 UTC · over 5 years ago
Public PoC available
Public proof-of-concept code published
-
04:20 UTC over 5 years ago04:20 UTC · over 5 years ago
CVE published
Vulnerability disclosed publicly
-
00:00 UTC over 5 years ago00:00 UTC · over 5 years ago
CVE ID reserved
Identifier reserved by the CNA
Automate This Intelligence with the Pro API
Confidence scoring, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.
Pro API Example
GET /api/v2/pro/kevs/CVE-2021-3493
{
"cve_id": "CVE-2021-3493",
"title": "The overlayfs implementation in the linux kernel did not properly validate wi...",
"affected_vendor": "Ubuntu",
"affected_product": "linux kernel",
"affected_versions": [
{ "vendor": "...", "product": "...", "status": "affected", "display_label": "..." }
],
"confidence": "Confirmed",
"cvss_score": 8.8,
"epss_score": null,
"exploit_status": {
"exploited_in_the_wild": true,
"active_exploitation_observed": false
},
"sensor_telemetry": { "...": "Pro API fields" },
"proof_of_concepts": [ "..." ],
"scanner_integrations": [ "..." ]
}