Some days ago I taught myself a little about NFQUEUE and Python. Meanwhile I dug a little more into the matter and looked into building new network packets. In this special case I wanted to create DNS packets. The idea was to intercept DNS requests with Netfilter and return a fake IP address in a faked DNS response. Messing with packets in Python is quite easy to do when you use the Python bindings for Scapy, a quite powerful packet manipulation tool. Read more

For the project of one of my students we need to intercept and modify SIP messages. Our first idea was to configure a proxy in the SIP user agent (soft phone) and to modify an existing SIP proxy to our liking. Unfortunately this approach did not work reliably as the soft phone seemed to be faulty: some SIP messages were sent via the proxy we configured, other were sent directly to the server. Read more