GDM is the GNOME display manager.
GDM allows a normal user to access the configuration manager.
When the "face browser" in GDM is enabled, a normal user can use the "configure login manager" with his/her own password instead of the root password, and thus gain additional privileges.
There is no known workaround at this time.
All GDM users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=gnome-base/gdm-2.8.0.8"