The lxc-sshd template (templates/lxc-sshd.in) in LXC before 1.0.0.beta2 uses read-write permissions when mounting /sbin/init, which allows local users to gain privileges by modifying the init file.
https://github.com/dotcloud/lxc/pull/1
https://bugs.launchpad.net/ubuntu/%2Bsource/lxc/%2Bbug/1261045