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June 2003

POF fingerprint scanning tools mitigate OS fingerprinting vulnerabilities

Tools that do operating system fingerprinting are a hacker's dream. They make it ridiculously simple to identify easy targets. Run Nmap against a target, learn what OS version it's running, and then look for a set of attack tools that can take out that particular release. If you place a POF sensor near one of your outgoing network connections, you can quickly build a map of machines and their OSes. Fortunately for us (the good guys), most fingerprinting scans leave distinctive patterns that are easily detected by a decent IDS. But aside from that, the good guys can also use a powerful OS fingerprinting technique called Passive Operating System Fingerprinting (POF). Several POF tools are available; the original is called "p0f" (with a zero), co-created by Michael Zalewski and Bill Stearns. POF is invisible, silent and nonintrusive. Unlike active fingerprinting tools such as Nmap, POF operates only as a sniffer and generates no packets. This is extremely important, because that means it won't interfere with legitimate traffic, and...

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