Directory traversal flaw was found in lxc.
As reported in http://seclists.org/oss-sec/2015/q3/648 :

"If an attacker constructs a malicious symlink in the target path of a container mount point, the symlink could be mishandled the next time the container is started and the mount operation may be performed at an undesired target location.

Additionally, if the source path of the mount is a malicious symlink relative to the container, the symlink could be mishandled to bind mount an undesired file or directory into the container.

Direct modification of the host's mount table is not possible since a slave copy of the mount table is used.

An example of an attack that is made possible by this flaw is a user inside of the container could leave behind a malicious symlink, at a mount point target under their control, that would cause /proc/self/attr to be mounted over. lxc-start would then unknowingly write to a "fake" /proc/self/attr/current file, prior to launching the container init, to perform an AppArmor profile transition. The profile transition would not occur and the container init would run under incorrect confinement."

Upstream patch:

https://github.com/lxc/lxc/commit/592fd47a6245508b79fe6ac819fe6d3b2c1289be