A security issue was found in Linux kernel’s OverlayFS subsystem where a
local attacker who has the ability to mount the TmpFS filesystem with
OverlayFS can abuse a logic bug in the overlayfs code which can
inadvertently reveal files hidden in the original mount.

Alois Wohlschlager discovered that the overlay file system in the Linux
kernel did not restrict private clones in some situations. An attacker
could use this to expose sensitive information.