Re: Firewall bypassing tool

From: Fyodor (fyodorat_private)
Date: Mon Nov 04 2002 - 10:07:44 PST

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    On Sun, Nov 03, 2002 at 05:02:49PM -0600, Frank Knobbe wrote:
    > On Fri, 2002-11-01 at 13:38, Michael Katz wrote:
    > > At 11/1/2002 03:28 AM, d_fence wrote:
    > > 
    > > One of the options for scanning is -sF, which will send SYN-FIN 
    > > packets.  You can also use -sA, which will send SYN-ACK packets.
    > 
    > I was about to post the same, but thought I validate first. To me it
    > seemed that nmap sends a packet with the FIN flag set. I did not see the
    > SYN flag set in addition to FIN, so nmap is not an answer to his
    > question.
    
    Nmap has an undocumented --scanflags option which allows you to
    specify arbitrary flags using the flag names or a number.  Thus a
    SYN-FIN scan can be done as follows:
    
    felix~#nmap -sS --scanflags SYNFIN -O db
    
    Starting nmap V. 3.10ALPHA3 ( www.insecure.org/nmap/ )
    Interesting ports on db.yuma.net (192.168.0.4):
    (The 1601 ports scanned but not shown below are in state: closed)
    Port       State       Service
    22/tcp     open        ssh                     
    111/tcp    open        sunrpc                  
    1024/tcp   open        kdm                     
    Remote operating system guess: Linux Kernel 2.4.0 - 2.5.20
    Uptime 58.471 days (since Fri Sep  6 23:45:12 2002)
    
    Nmap run completed -- 1 IP address (1 host up) scanned in 10.651
    seconds
    
    Note that "-sS" causes this scan to use "SYN Scan" semantics (eg
    treating SYN|ACK responses as open ports).  For FIN scan semantics
    (dropped packets signify open ports, RST for closed ones) just specify
    "-sF" instead.
    
    Cheers,
    Fyodor
    



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