I may be missing something, but whenever I display (or try to change) the IP address associated with a veth (for a container) it shows as 0.0.0.0/0 in WinBox and as a "blank" in WebFig.

Is this a bug or I'm really missing something here?

Thanks in advance.

What version?
I think this is due to adding IPv6 support for VETH.
You can check with "interface/veth/print" in the terminal. If you close the window in the Winbox and don't click OK or Apply, It should work as expected.

WinBox is 3.39 and WebFig 7.11.1 (latest as of this post).

Yes, it is correct when using the CLI.

Your WinBox image show exactly what I'm talking about: Address: 0.0.0.0/0.

It's not a question of being able to check the IP address using WinBox/WebFig, but rather to make changes (need apply/ok).

Look what happens when you modify (webFig) a veth interface and "reenter" the IP address:

[admin@gaia] > /interface/veth/print
Flags: X - disabled; R - running
0 ;;; test
name="veth1" address=10.10.10.248/0,10.10.10.249/0,192.168.55.1/0
gateway=10.10.10.1 gateway6=""

It ADDs the IP to making it a list... Weird, at best. This is definitely a bug

WinBox at least does not create multiple addresses (edited the last veth to force a change):

[admin@gaia] > /interface/veth/print
Flags: X - disabled; R - running
0 ;;; test
name="veth1" address=10.10.10.247/32 gateway=10.10.10.1 gateway6=""

Strangely is that after changing with WinBox, if I open the veth again it shows the IP. But it will revert to 0.0.0.0/0 if I close and reopen WinBox (so it was kept in memory on WinBox).

A clear bug for me.

Hi I confirm this, same issue.
Is MikroTik aware?

Hello, here too, but I "solved" this problem.

1. Remove the container
2. Set veth interface, ex: 10.11.12.10/24
3. Add the container again

Have the same problem, it is working some time but i think after an reboot the problems always starts

Once the VETH "goes bad", I've seen it stay bad. You can also delete the VETH interface and re-create it again, then reference the new VETH in container (instead of re-creating container). That's fixed similar VETH issues in past for me.

There are been various bugs/etc in previous versions with VETH that seem to happen in some cases. I do think 7.12rc does seem better with VETH, so hopeful it's more stable in future.