Ah can’t believe I haven’t posted about this one before, one of my favourite tools! It was a big breakthrough to have a passive OS-fingerprinting tool after relying on Nmap and Xprobe2 for the longest time.

OS fingerprinting is a very important part of a pen-test during the information gathering stage.

P0f v2 is a versatile passive OS fingerprinting tool. P0f can identify the operating system on:

• machines that connect to your box (SYN mode),
• machines you connect to (SYN+ACK mode),
• machine you cannot connect to (RST+ mode),
• machines whose communications you can observe.

P0f can also do many other tricks, and can detect or measure the following:

• firewall presence, NAT use (useful for policy enforcement),
• existence of a load balancer setup,
• the distance to the remote system and its uptime,
• other guy’s network hookup (DSL, OC3, avian carriers) and his ISP.

All this even when the device in question is behind an overzealous packet firewall, when our favourite active scanner can’t do much. P0f does not generate ANY additional network traffic, direct or indirect. No name lookups, no mysterious probes, no ARIN queries, nothing. How? It’s simple: magic. Find out more here.

P0f is quite useful for gathering all kinds of profiling information about your users, customers or attackers (IDS, honeypot, firewall), tech espionage (laugh…), active or passive policy enforcement (restricting access for certain systems or otherwise handling them differently; or detecting guys with illegal network hookups using masquerade detection), content optimization, pen-testing (especially with SYN+ACK and RST+ACK modes), thru-firewall fingerprinting… plus all the tasks active fingerprinting is suitable for. And, of course, it has a high coolness factor, even if you are not a sysadmin.

P0f v2 is lightweight, secure and fast enough to be run almost anywhere, hands-free for an extended period of time.

You can donwload p0f v2 here:

p0f.tgz
p0f for Windows

Or read more here.