Updated GDM packages has been released for both Ubuntu Linux 18.04 LTS and 18.10

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Ubuntu Security Notice USN-3892-1
February 20, 2019

gdm3 vulnerability
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 18.10
- Ubuntu 18.04 LTS

Summary:

GDM could give unauthorized access to a different user.

Software Description:
- gdm3: GNOME Display Manager

Details:

Burghard Britzke discovered that GDM incorrectly handled certain
configurations. An attacker could possibly use this issue to get
unauthorized access to a different user.

Update instructions:

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

Ubuntu 18.10:
  gdm3 3.30.1-1ubuntu5.1

Ubuntu 18.04 LTS:
  gdm3 3.28.3-0ubuntu18.04.4

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

References:
  https://usn.ubuntu.com/usn/usn-3892-1
  CVE-2019-3825

Package Information:
  https://launchpad.net/ubuntu/+source/gdm3/3.30.1-1ubuntu5.1
  https://launchpad.net/ubuntu/+source/gdm3/3.28.3-0ubuntu18.04.4

  GDM Security Update for Ubuntu 18.04/18.10