A gdm3 security update has been released for Debian GNU/Linux 9 LTS to address an issue where GNOME Display Manager not detecting any users may make GDM launch initial system setup and thereby permitting the creation of new users with sudo capabilities.

DLA 2434-1: gdm3 security update

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Debian LTS Advisory DLA-2434-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Chris Lamb
November 05, 2020   https://wiki.debian.org/LTS
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Package : gdm3
Version : 3.22.3-3+deb9u3
CVE ID : CVE-2020-16125

It was discovered that there was an issue in the GNOME Display
Manager where not detecting any users may make GDM launch initial
system setup and thereby permitting the creation of new users with
sudo capabilities.

For Debian 9 "Stretch", this problem has been fixed in version
3.22.3-3+deb9u3.

We recommend that you upgrade your gdm3 packages.

For the detailed security status of gdm3 please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/gdm3

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://wiki.debian.org/LTS