While upgrading the package, post_service results in calling pmap_dump:

apt-get---sh---post_service---service---portmap---pmap_dump

which then hangs on an attempt to connect to a system's external IP which is
firewalled down:

connect(3, {sa_family=AF_INET, sin_port=htons(111),
sin_addr=inet_addr("a.b.c.d")}, 16

Disabling iptables for a few seconds results in successful exit.

It was mentioned that pmap_dump should attempt a connection to 127.0.0.1, not
any other IP on the system.