CVE-2021-3493

Exp

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.

Published: 2021-04-17 Last update: 2025-10-28 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3493 is rated Critical Active Threat (95.2/100): CVSS High severity, with high exploitation likelihood (EPSS 79.96%, 99th percentile). CISA KEV confirms active exploitation (added 2022-10-20) affecting Linux / Kernel. a weakness (CWE-270) Unauthenticated remote administrative access may be possible. The CISA remediation deadline has passed—treat as an emergency patch priority.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

CISA KEV Record for CVE-2021-3493

Name: Linux Kernel Privilege Escalation Vulnerability · CISA KEV detail

Exploit added: 2022-10-20

Action due: 2022-11-10

Required action: Apply updates per vendor instructions.

Public exploit references (Exploit-DB) for CVE-2021-3493

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-3493

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-07 79.71% 79.96% +0.26%
2 2026-05-22 76.89% 79.71% +2.81%
3 2026-05-16 — 76.89% —

Full EPSS history (86 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3493

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.8 3.1 HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.0 6.0 [email protected]
7.8 3.1 HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 5.9 [email protected]
7.2 2.0 HIGH
AV:L/AC:L/Au:N/C:C/I:C/A:C Click to expand
Access vector (AV:L)
Requires local access to the target system.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:C)
Complete confidentiality impact.
Integrity impact (I:C)
Complete integrity impact.
Availability impact (A:C)
Complete availability impact.
 3.9 10.0 [email protected]

Weakness enumeration for CVE-2021-3493

OS Trackers for CVE-2021-3493

vendor priority summary link
debian not yet assigned CVE-2021-3493 not yet assigned priority: Debian including 1 source packages (linux), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-3493
redhat medium — https://access.redhat.com/security/cve/CVE-2021-3493
suse high CVE-2021-3493 severity important: SUSE including 13 source package names (kernel-default, kernel-default-base, …), 201 product×package rows across 44 product lines (HPE Helion OpenStack 8, SUSE CaaS Platform 4.0, … (44 product lines)): Known Not Affected 201. https://www.suse.com/security/cve/CVE-2021-3493/
ubuntu high CVE-2021-3493 high priority: Ubuntu including 169 source packages (linux, linux-allwinner, …), 2181 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1696, not-affected 233, released 216, ignored 36. https://ubuntu.com/security/CVE-2021-3493

Affected software / configurations for CVE-2021-3493

Vendor Product Version Raw CPE
canonical ubuntu_linux < 18.04 cpe:2.3:o:canonical:ubuntu_linux:*:*:*:*:lts:*:*:*
canonical ubuntu_linux >= 18.04.1, < 20.04 cpe:2.3:o:canonical:ubuntu_linux:*:*:*:*:lts:*:*:*
canonical ubuntu_linux < 20.10 cpe:2.3:o:canonical:ubuntu_linux:*:*:*:*:-:*:*:*

References for CVE-2021-3493

URL Tags
http://packetstormsecurity.com/files/162434/Kernel-Live-Patch-Security-Notice-LSN-0076-1.html Exploit Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/162866/Ubuntu-OverlayFS-Local-Privilege-Escalation.html Press/Media Coverage Third Party Advisory VDB Entry
http://packetstormsecurity.com/files/165151/Ubuntu-Overlayfs-Local-Privilege-Escalation.html Exploit Third Party Advisory VDB Entry
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52 Mailing List Patch Third Party Advisory
https://ubuntu.com/security/notices/USN-4917-1 Vendor Advisory
https://www.openwall.com/lists/oss-security/2021/04/16/1 Mailing List Third Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3493 US Government Resource
cvelogic Threat Intelligence