A vulnerability was discovered in gdm when timed login is enabled in configuration. An attacker could bypass the lock screen by selecting the timed login user and waiting for the timer to expire at which time they would gain access to the logged-in user's session.
Under the right circumstances, after the timed login timeout expires, a running session may get misassociated with the timed login user instead of the user that started the session. Further attempts to log in as the timed login user will instead unlock the misassociated user session.
This only affects X.org since, gdm kills the login screen on wayland after login.
Timed logins must be enabled to expose this vulnerability.
Name: the GNOME Project
Upstream: Burghard Britzke
Ensure timed login is not enabled in gdm configuration, by checking the output of:
grep TimedLogin /etc/gdm/custom.conf
Created gdm tracking bugs for this issue:
Affects: fedora-all [bug 1672830]