attach.c in LXC 1.1.2 and earlier uses the proc filesystem in a container, which allows local container users to escape AppArmor or SELinux confinement by mounting a proc filesystem with a crafted (1) AppArmor profile or (2) SELinux label.
https://service.ait.ac.at/security/2015/LxcSecurityAnalysis.html
https://github.com/lxc/lxc/commit/5c3fcae78b63ac9dd56e36075903921bd9461f9e
http://www.ubuntu.com/usn/USN-2675-1
http://www.securityfocus.com/bid/75998
http://www.debian.org/security/2015/dsa-3317
http://lists.opensuse.org/opensuse-updates/2015-07/msg00067.html
http://lists.opensuse.org/opensuse-updates/2015-07/msg00066.html
http://lists.opensuse.org/opensuse-security-announce/2019-05/msg00073.html