LXC can steal IP Addresses

[daniel_wwf]

Hey,

I have a /24 connected to a host. If I fire up a LXC with and assign an IP to it eg: 10.10.10.10 (just an example) the guest is able to steal an address like 10.10.10.11 by just changing it interfaces config and restarting the network. We activated the FW and tried using IPSet to prevent this from happening, however, no matter what we do, it's still possible.

What would be the correct way to make sure that's not possible anymore?

 

[t.lamprecht]

A simple solution would be to change the CTs default OUTPUT policy to REJECT or DROP and add an accept rule for out= 10.10.10.10 to the CTs firewall ruleset.

Ensure that the Firewall is on on the Datacenter, the CTs Firewall Option Tab and the CTs Network veth device (in the Network Tab).
You can check with

iptables-save

if it got applied, may want to grep for "veth" or "vethVMID" to find it quickly.

With this, all network packets which do not come from your whitelisted IP address will get rejected/dropped.

 

[t.lamprecht]

Or, alternatively, keep OUTPUT policy on "ACCEPT" and enable the "IP Filter" option in the containers firewall options tab.