Local privilege escalation via namespace capability validation
Published Apr 17, 2021 · Updated Oct 21, 2025
Privilege escalation in affected Ubuntu Linux kernels allows local users to gain root access through an unprivileged OverlayFS mount. OverlayFS permits a user-namespace process to set file capabilities on an underlying file without converting the capability metadata for the target namespace. Exploitation requires local low-privileged access, unprivileged user namespaces, and an Ubuntu patch permitting unprivileged OverlayFS mounts; unaffected upstream kernels lack that combination.
Summary
What happened
Privilege escalation in affected Ubuntu Linux kernels allows local users to gain root access through an unprivileged OverlayFS mount. OverlayFS permits a user-namespace process to set file capabilities on an underlying file without converting the capability metadata for the target namespace. Exploitation requires local low-privileged access, unprivileged user namespaces, and an Ubuntu patch permitting unprivileged OverlayFS mounts; unaffected upstream kernels lack that combination.
The record
- CVE
- CVE-2021-3493
- Published
- Apr 17, 2021
- Updated
- Oct 21, 2025
- Vendor
- Linux Foundation
- Product
- Linux Kernel
- Classifications
- CWE-270, CWE-863, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 17, 2021CVE publishedPublication date reported by the CVE source.
- Oct 20, 2022Exploitation reportedCISA Known Exploited Vulnerabilities Catalog entry
- Oct 21, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=4.15 kernel <4.15.0-142.146
- Affected versionversion=4.4 kernel <4.4.0-209.241
- Affected versionversion=5.4 kernel <5.4.0-72.80
- Affected versionversion=5.8 kernel <5.8.0-50.56
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Ubuntu OverlayFS Local Privilege Escalation proof of conceptproof of concept · unverified
- Metasploit Ubuntu OverlayFS local privilege escalation moduleweaponized · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Reported exploitation
- CISA Known Exploited Vulnerabilities Catalog entryknown exploited catalog
Technologies
Your stack
See the directory against your own environment.
Your stack
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