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Hack Security Pro.pdf - Index of

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We know that the server <strong>of</strong> interest to us, port 21, is closed. So we will repeat the same method by<br />

exchanging port 22 for port 21. Let us take a look at the results.<br />

First terminal: emission <strong>of</strong> spo<strong>of</strong>ed packets to server S.<br />

Second terminal : emission <strong>of</strong> TCP/IP packets to client C.<br />

Here, we can see that the ID has not changed. Why? Because a machine never responds to a Reset.<br />

When a port is closed, there is no “leaking” <strong>of</strong> packets, so there are no more modifications <strong>of</strong> the ID.<br />

You probably understand now how vitally important it is that machine C communicate only with A.<br />

Conclusion<br />

In this chapter, we seen the functioning principle <strong>of</strong> this type <strong>of</strong> scan.<br />

Please note that Unix users make use <strong>of</strong> the famous fyodor (nmap) port scanner (downloadable at<br />

http://www.insecure.org). It takes into account this type <strong>of</strong> scan and can be very powerful. You will also<br />

note that even if you are not in S's logs, you are in those <strong>of</strong> C. So a hacker can be found...<br />

The <strong>Hack</strong>ademy DMP -88/209- SYSDREAM

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