Documentation says the pg_cancel_backend role cannot
signal "a backend owned by a superuser". On the
contrary, it can signal background workers, including
the logical replication launcher. It can signal
autovacuum workers and the autovacuum launcher.
Signaling autovacuum workers and those two launchers
provides no meaningful exploit, so exploiting this
vulnerability requires a non-core extension with a
less-resilient background worker. For example, a
non-core background worker that does not auto-restart
would experience a denial of service with respect to
that particular background worker.