LXDM before 0.5.2 did not start X server with -auth, which allows local users to bypass authentication with X connections.
{ "availability": "No subscription required", "ubuntu_priority": "high", "binaries": [ { "binary_name": "lxdm", "binary_version": "0.5.3-1" }, { "binary_name": "lxdm-dbg", "binary_version": "0.5.3-1" }, { "binary_name": "lxdm-dbgsym", "binary_version": "0.5.3-1" } ] }