gdm3 versions before 3.36.2 or 3.38.2 would start gnome-initial-setup if gdm3 can't contact the accountservice service via dbus in a timely manner; on Ubuntu (and potentially derivatives) this could be be chained with an additional issue that could allow a local user to create a new privileged account.
https://securitylab.github.com/advisories/GHSL-2020-202-gdm3-LPE-unresponsive-accounts-daemon