Vulnerability Report

CVE-2021-3493

CISA KEV Active

Title: Overlayfs Privilege Escalation via User Namespaces

Privilege Escalation

Proof Of Concept

PoC Available for CVE-2021-3493

CWE Category CWE-863
Published Date Apr 17, 2021
Modified Date Oct 28, 2025
Exploit Status Available
Score 8.8 CVSS v3.1
Exploit Probability (EPSS)
43.99%

Vulnerability Summary

CVE-2021-3493: 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.

Impacted Vendors

U
ubuntu 1
C
canonical 1

Reference Links

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://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52 https://ubuntu.com/security/notices/USN-4917-1 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://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9988a39d52 https://ubuntu.com/security/notices/USN-4917-1 https://www.openwall.com/lists/oss-security/2021/04/16/1 https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-3493
CVSS v3.1
Source Entity [email protected]
Severity HIGH
8.8
Attack Vector
LOCAL
Complexity
LOW
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
CHANGED
RAW VECTOR CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
CVSS v3.1
Source Entity [email protected]
Severity HIGH
7.8
Attack Vector
LOCAL
Complexity
LOW
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS v2.0
Source Entity [email protected]
Severity HIGH
7.2
Access Vector
N/A
Authentication
N/A
RAW VECTOR AV:L/AC:L/Au:N/C:C/I:C/A:C

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2021-3493 Exploits & PoCs (Proof Of Concept)

GitHub https://github.com/briskets/CVE-2021-3493
View Code
GitHub https://github.com/inspiringz/CVE-2021-3493
View Code
GitHub https://github.com/oneoy/CVE-2021-3493
View Code
MODIFIED

Vulnerability data or affected products updated.

PUBLISHED

Vulnerability first announced in NVD.

Attack Vector Matrix

Access Vector LOCAL
Complexity LOW
Privileges N/A
Interaction NONE
CVSS Vector String CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Affected Stack

No specific products linked.