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Network Security Pen-Test
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Re: Blocking Port scans

Subject: Re: Blocking Port scans
Date: Thu, 27 Oct 2005 08:47:52 +0300
BSK wrote:

Hello Everyone,

Just wanted some feedback from you people. I'm doing a
Firewall Assessment for a CISCO PIX firewall. The
firewall allows SYN, FIN, NULL and XMAS scans but
blocks ACK scans (largely means its a stateful
firewall).

Now what do we do to block the scans that are allowed.
I think it should be easy to block FIN, NULL and XMAS
scans but how do we block or limit or workaround a SYN
scan. 1 way that I think is probably blocking or
limiting  the packets from the source (using IDS/IPS)

Looking ahead to some ideas, thoughts, hints.

thns bshan



Hello,

I think that wasting your time searching for a (complex?) mechanism to block port scans is useless.
If a person wants to know what services a host is running - he will find them ... one way or another.


Nmap for example has alot of options that can make any port scan detecting system suffer: decoys,
paranoid scanning option, etc .. etc. But maybe a person doesn't even need the internet to figure out
the services - there are phones, not so knowledgable support personnel, etc.


I would prefer researching and intergrating more serious and interesting security policies
than wondering how to block port scans.


Otherwise if you still insist on trying to detect port scans (and block them after that),
you can try scanlogd by Solar Designer.


Maybe i get the whole picture wrong and my opinion is useless, you will decide that ;-)


regards, Georgi Alexandrov

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