RE: Blocking Port scans

["Geelen, Ruud" <ruud.geelen () logicacmg com>]

Hi all,

I agree with Georgi: it is not a function of a firewall to block /
detect port scans. The PIX is designed to protect your network. So
(D)DOS attacks would be blocked by your firewall if configured correctly
amongst other things. (using the "static" commands) 
Scans are noticed but if legitimate not blocked.

If you want to detect port scans you need IDS functionality, if you need
to block it think about an IPS. Your PIX will not let you do this, the
IDS it uses is much to weak to do so (version 6.3 and below), although
since v7.x a lot has changed.
And even there: if it is a very slow scan not many IDS/IPS will detect
them.

So forget about being able to block port scans on a firewall and think
about IDS/IPS equipment.

Cheers,
Ruud
CCIE #12793 security

-----Original Message-----
From: Georgi Alexandrov [mailto:georgi.alexandrov () gmail com] 
Sent: donderdag 27 oktober 2005 7:48
To: pen-test () securityfocus com
Subject: Re: Blocking Port scans

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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