USN-3285-1: LightDM vulnerability

12 May 2017

lightdm vulnerability

A security issue affects these releases of Ubuntu and its derivatives:

  • Ubuntu 17.04
  • Ubuntu 16.10


LightDM could allow unintended access to files.

Software Description

  • lightdm - Display Manager


Tyler Hicks discovered that LightDM did not confine the user session for guest users. An attacker with physical access could use this issue to access files and other resources that they should not be able to access. In the default installation, this includes files in the home directories of other users on the system. This update fixes the issue by disabling the guest session. It may be re-enabled in a future update. Please see the bug referenced below for instructions on how to manually re-enable the guest session.

Update instructions

The problem can be corrected by updating your system to the following package versions:

Ubuntu 17.04
lightdm - 1.22.0-0ubuntu2.1
Ubuntu 16.10
lightdm - 1.19.5-0ubuntu1.2

To update your system, please follow these instructions:

After a standard system update you need to reboot your computer to make all the necessary changes.