fs/namespace.c in the Linux kernel before 4.0.2 processes MNT_DETACH umount2 system calls without verifying that the MNT_LOCKED flag is unset, which allows local users to bypass intended access restrictions and navigate to filesystem locations beneath a mount by calling umount2 within a user namespace.
Severity
CVSS 3.0
6.1 medium
CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N
EPSS
0.3% chance of exploitation in the next 30 days; higher than 26% of CVEs (scores of 2026-10-31)