If I set CONFIGURE_INTERFACES=no in /etc/default/networking and
disable all in /etc/network/interfaces, then the interfaces are
still brought up (even for systemd.unit=rescue).

On bringing up eth0 in a traditional IPv6 network with router
advertisement daemon the interface automatically gets an (unwanted)
global routable IPv6 address. This potentially introduces a conflict
with the configuration in /etc/network/interfaces, network-manager
(if installed) and it might have security implications (e.g. firewall
not configured yet, mac address exposed, etc.).

In Wheezy this configure option is not ignored.

I can also delete /etc/network/interfaces, and yet lo and eth0
are brought up, so I am not quite sure if this is an issue of
ifupdown. Please reassign, if necessary.


Regards
Harri

Since this bug has security implications, would you mind to
increase the priority?

Thanx
Harri

CONFIGURE_INTERFACES only influences whether interfaces that are "auto"
are started at boot. It doesn't change how "allow-hotplug" interfaces
are brought up. What does your /etc/network/interfaces look like?

Also, do you still have the problem with recent versions of ifupdown?

If it's still brought up when there is no /etc/network/interfaces, then
it's not ifupdown who is configuring the interface. I cannot reassign
the bug, because I don't know which package does configure your eth0,
and in any case, that package would not read /etc/default/networking
anyway.