libpq looks a connection service up in the service file of the operating-system account running pgAdmin 4, and an entry there can hold a password or name a password file or client certificate. In server mode any user could set a server's Service, or a "service" connection parameter, to one of those entries and connect with its credentials. A PGPASSWORD or PGSERVICE variable set for that account was likewise used by libpq for every connection without a value of its own and passed on to the utilities, and pg_dumpall read a maintenance database name such as "service=..." as a connection string. The fix adds the SERVER_MODE_ALLOWED_SERVICES setting, empty by default: in server mode only a listed