CVE-2021-3493: Linux Kernel Privilege Escalation Vulnerability

High severity, CVSS 7.8. Actively exploited: in CISA KEV since 2022-10-20. EPSS: 49.2% chance of exploitation in the next 30 days.

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.

Affected products

• Canonical Ubuntu Linux: before 18.04 (fixed in 18.04); from 18.04.1, before 20.04 (fixed in 20.04); before 20.10 (fixed in 20.10)

Published 2021-04-17. Last modified 2026-06-17.