Linux · Kernel
CVE-2021-3493
Linux Kernel Privilege Escalation Vulnerability
What it is
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.
CISA: 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.
What to do
Apply updates per vendor instructions.
Deadline for US federal agencies: November 10, 2022
- Added to the CISA list
- October 20, 2022
- Published
- April 17, 2021
- Severity
- High 8.8 CVSS 3.1
- Chance of attacks in the next 30 days (EPSS)
- 49% in the top 1.1% of all known vulnerabilities
- Weakness
- CWE-862
- More details
- NVD · CVE.org · CISA
All references (6)
- https://ubuntu.com/security/notices/USN-4917-1
- https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c03e2cda4a584cadc398e8f6641ca9…
- 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
More exploited flaws from Linux
| Added | Vulnerability | Product | Severity | Attack chance |
|---|---|---|---|---|
| Sep 18, 2026 | Improper Check for Unusual or Exceptional Conditions | Kernel | Critical 9.8 | 3.3% |
| Sep 18, 2026 | Race Condition | Kernel | High 7.8 | 1.6% |
| Sep 18, 2026 | Out-of-Bounds Write | Kernel | High 8.8 | 0.9% |
| Aug 27, 2026 | Unspecified | Kernel | High 7.8 | 0.7% |
| Aug 26, 2026 | Out-of-Bounds Write | Kernel | High 7.8 | 8.9% |
| Jun 2, 2026 | Improper Authentication | Kernel | High 7.8 | 5.5% |
| May 1, 2026 | Incorrect Resource Transfer Between Spheres | Kernel | High 7.8 | 98% |
| Jan 26, 2026 | Integer Overflow | Kernel | High 7.8 | 15% |
Sources: Known Exploited Vulnerabilities (CISA, public domain), CVE records (cve.org) and EPSS (FIRST). The chance of attacks is the EPSS estimate that someone will try to exploit the flaw in the next 30 days.