Exploitation evidence
Known exploited · CISA KEV listed
Added 2022-10-20. Ransomware campaign use: Unknown.
CISA required action: Apply updates per vendor instructions.
CISA due date: 2022-11-10. This is the catalog’s deadline, not an assessment of your organization’s exposure.
KEV checked 13 Nov 2026, 00:20 Jerusalem · Original catalog ↗Reported products and versions
Ubuntu / linux kernel
Default status: Not specified
- affected: 5.8 kernel to < 5.8.0-50.56 (custom)
- affected: 5.4 kernel to < 5.4.0-72.80 (custom)
- affected: 4.15 kernel to < 4.15.0-142.146 (custom)
- affected: 4.4 kernel to < 4.4.0-209.241 (custom)
Fixes and workarounds
Apply https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52
Reported workarounds: Disable unprivileged user namespaces.
Sources and related reporting
CVE Program record ↗ · Download tracked evidence as JSON
- https://ubuntu.com/security/notices/USN-4917-1
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52
- https://www.openwall.com/lists/oss-security/2021/04/16/1
- http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.html
- http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.html
- http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.html
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3493
Observed change timeline
History begins when Egret first downloads each source. It is not the complete upstream CVE history.
12 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-12",
"epss": 0.49166,
"percentile": 0.98902
}10 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-10",
"epss": 0.49166,
"percentile": 0.98894
}09 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-09",
"epss": 0.49166,
"percentile": 0.98892
}08 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-08",
"epss": 0.49166,
"percentile": 0.98892
}07 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-07",
"epss": 0.49166,
"percentile": 0.98892
}06 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-06",
"epss": 0.49166,
"percentile": 0.9889
}06 Nov 2026, 06:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-05",
"epss": 0.49166,
"percentile": 0.98889
}05 Nov 2026, 12:20 Jerusalem · CVE Program record changed
Stored CNA snapshot at this observation.
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}04 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
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"epss": 0.49166,
"percentile": 0.98888
}03 Nov 2026, 18:20 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
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"epss": 0.49166,
"percentile": 0.98886
}03 Nov 2026, 02:22 Jerusalem · EPSS observation updated
Stored EPSS snapshot at this observation.
{
"date": "2026-11-02",
"epss": 0.49166,
"percentile": 0.98884
}03 Nov 2026, 02:22 Jerusalem · CISA KEV status changed
Stored KEV snapshot at this observation.
{
"cveID": "CVE-2021-3493",
"cwes": [
"CWE-862"
],
"dateAdded": "2022-10-20",
"dueDate": "2022-11-10",
"forensicTriage": "No",
"knownRansomwareCampaignUse": "Unknown",
"notes": "https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52; https://nvd.nist.gov/vuln/detail/CVE-2021-3493",
"product": "Kernel",
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"shortDescription": "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.",
"vendorProject": "Linux",
"vulnerabilityName": "Linux Kernel Privilege Escalation Vulnerability"
}