Asymmetric Routing Around the Firewall

>Later, when I realized that inbound traffic was bypassing the firewall, I notified UC Berkeley’s Information Security Office of the potential security vulnerability, but their response was somewhat lacking in urgency. So we’ll see.

If I were on their infosec team I wouldn't ignore it, but also, infosec and network often different silos. If network was already notified, infosec can't do much but complain.

And, it seems the network was somewhat secure anyway. Any inbound scan or malicious traffic would get dropped going outbound, since there was no session on the outbound firewall.

I have run into this, and I got tipped off by the very specific session timeout that was set on the firewall. The session would come up and work for around 30 seconds, then stop. The outbound packets were going to the firewall but being returned from a different address on the same subnet. The firewall would stop forwarding the outbound packets after the session expired since it did not observe the session being established (as the reply packets did not traverse the firewall).

I would think that a network that even has a physical path capable of bypassing a firewall would be considered broken by design... Or at least insecure.

Glad you found out. Good job !

Also usually firewalls are not decreasing packets IP TTL which make them invisble to traceroute.

You are lucky this one does not.