CVE-2021-3492: Canonical Ubuntu Linux

High severity, CVSS 7.8. EPSS: 1.5% chance of exploitation in the next 30 days.

Shiftfs, an out-of-tree stacking file system included in Ubuntu Linux kernels, did not properly handle faults occurring during copy_from_user() correctly. These could lead to either a double-free situation or memory not being freed at all. An attacker could use this to cause a denial of service (kernel memory exhaustion) or gain privileges via executing arbitrary code. AKA ZDI-CAN-13562.

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.