Ubuntu Security Notice 3285-1 - 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.
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