In Kubernetes versions 1.3.x, 1.4.x, 1.5.x, 1.6.x and prior to versions 1.7.14, 1.8.9 and 1.9.4 containers using subpath volume mounts with any volume type (including non-privileged pods, subject to file permissions) can access files/directories outside of the volume, including the host's filesystem.
https://github.com/kubernetes/kubernetes/issues/60813
https://access.redhat.com/errata/RHSA-2018:0475
http://lists.opensuse.org/opensuse-security-announce/2020-04/msg00041.html