lxc-attach in LXC before 1.0.9 and 2.x before 2.0.6 allows an attacker inside of an unprivileged container to use an inherited file descriptor, of the host's /proc, to access the rest of the host's filesystem via the openat() family of syscalls. https://nvd.nist.gov/vuln/detail/CVE-2016-8649
