Specify IPSEC Interface instead of WAN Interface

Following setup:

(LAN1: 172.12.0.0/24) MT-ROS-1 <=> Internet <=> MT-ROS-2 (LAN2: 10.11.0.0/16)

I have an IPSEC VPN connection between this networks. Everything is working.

On the right site (MT-ROS-2) I have following firewall rule in the first line: (I have more, but this one is for interest)

/ip firewall filter
add in-interface=WAN out-interface=LAN src-address 172.12.0.0/24 dst-address=10.11.0.0/16 chain=forward action=accept

This is for VPN traffic from left to right.

Now my security question:

If someone has access to the provider router (the one that is my default gw at the provider) and give himself an IP address e.g. 172.12.0.123 and set a route to my Mikrotik
the above firewall rule would give him access to my LAN, right?

I know that this is an internal net (172.12.0.0/24) and they will not be routed through the internet. But someone could do this if he/she has access to the provider router (e.g. hacked).

How can I setup a firewall rule for VPN traffic, that doesn’t use the WAN interface (for me it’s a security problem)?

I know this from the Linux kernel 2.4 where you have to use e.g. the ipsec0 interface in the firewall rules.

Kind regards

Carsten