Python raw sockets sniffing & pcap saving

Posted: March 9, 2017 in security
Tags: , ,

Even though we are pretty used to it, libpcap is not always present on systems. Usually, regardless of your goal, looking at traffic is actually pretty useful. In my experience this applies to offensive (pentesting, red team) work as well as defensive (incident response, network monitoring) work.

One of the first things that comes to mind, when libpcap is not available, is of course raw sockets, since these seem to be always available as long as you have the correct privileges. I’ve written previously about them as well as created some POC for backdoor purposes. Up until now raw sockets haven’t failed me, so when during a recent assignment I had to sniff traffic without libpcap I decided to write some Python code to achieve this. In case you are wondering, yes this was to further gather juicy information from unencrypted protocols like telnet, http and ftp.

A script nowadays never starts without a quick google query to save yourself the trouble of writing everything from scratch. So even though I enjoy writing a lot of things from scratch to learn, in this case I mainly adjusted an excellent example script from: http://askldjd.com/2014/01/15/a-reasonably-fast-python-ip-sniffer/

Adjusting the above script to save the data in pcap format was an easy undertaking and immediately useful. After waiting for a couple of minutes I got myself a nice pcap file which I could analyse on another machine with regular tools like tcpdump or wireshark.

You can find the script on the following gist

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