libcontainer/user/user.go in runC before 0.1.0, as used in Docker before 1.11.2, improperly treats a numeric UID as a potential username, which allows local users to gain privileges via a numeric username in the password file in a container.
https://security.gentoo.org/glsa/201612-28
https://github.com/opencontainers/runc/releases/tag/v0.1.0
https://github.com/opencontainers/runc/pull/708
https://github.com/opencontainers/runc/commit/69af385de62ea68e2e608335cffbb0f4aa3db091
https://github.com/docker/docker/issues/21436
http://rhn.redhat.com/errata/RHSA-2016-2634.html
http://rhn.redhat.com/errata/RHSA-2016-1034.html
http://lists.opensuse.org/opensuse-updates/2016-05/msg00111.html