Home page logo
/

pen-test logo Penetration Testing mailing list archives

Re: nmap and icmp-replies
From: Meier Zwei <meier_zwei () gmx net>
Date: Fri, 21 Apr 2006 10:32:30 +0200

> So don't filter these messages, they make your scan results much more
> reliable.

As far as UDP is concerned I agree. But a box sending those icmp-replies to rate-limit TCP-connects obviously brings nmap to slow down dramatically. nmap should ignore icmp-replies when scanning only TCP, as TCP doesn't need icmp to rate traffic (AFAIU).


Meier


Tobias Glemser schrieb:
> Meier,
>
> ICMP Dest-Unreachable should occur when scanning UDP. Since UDP is
> stateless, it's the only way a stack can "tell" a port is
> closed/filtered. Even if you send a packet to an open UDP Port,
> depending on the protocol your scanner has to send a valid payload to
> get an answer. If your target sends ICMP Dest-Unrecheachables, you
> should feel lucky.
> If an UDP Port is open your scanner will recognize this, because it
> doesn't matter which payload it sends: If there is no service, it will
> receive the Dest-Unreachable Packet, if there is any service, it won't.
> Conclusion: This port is open.
>
> So don't filter these messages, they make your scan results much more
> reliable.
>
> To answer your question: There is no way to tell nmap to ignore ICMP
> Answers. A iptabled gateway between your system and the target will help
> reaching your questionable goal.
>
> Cheers,
>
> Toby
>
> Meier Zwei wrote on 19.04.2006 14:26:
>> Hi list,
>>
>> while scanning somes hosts I figured out that a scanned packet filter
>> sending back icmp destination-unreachable rather slow forces nmap to
>> slow down scanning. A packet filter just dropping the scan probes has
>> no effect on nmap, so does a host without any packet filter, just
>> sending RST.
>> My problem is: filtering out the icmp answers with iptables doesn't
>> work, as nmap seems to hook into the kernel before iptable does. Is
>> there any to tell nmap to ignore icmp replies and just to determine a
>> port status via TCP/UDP?
>>
>> Thanks in advance
>>
>> Meier
>>
>> ------------------------------------------------------------------------------
>>
>> This List Sponsored by: Cenzic
>>
>> Concerned about Web Application Security? Why not go with the #1
>> solution - Cenzic, the only one to win the Analyst's Choice Award from
>> eWeek. As attacks through web applications continue to rise, you need
>> to proactively protect your applications from hackers. Cenzic has the
>> most comprehensive solutions to meet your application security
>> penetration testing and vulnerability management needs. You have an
>> option to go with a managed service (Cenzic ClickToSecure) or an
>> enterprise software (Cenzic Hailstorm). Download FREE whitepaper on
>> how a managed service can help you:
>> http://www.cenzic.com/news_events/wpappsec.php And, now for a limited
>> time we can do a FREE audit for you to confirm your results from other
>> product. Contact us at request () cenzic com for details.
>> ------------------------------------------------------------------------------
>>
>>
>>
>
> ------------------------------------------------------------------------------
>
> This List Sponsored by: Cenzic
>
> Concerned about Web Application Security? Why not go with the #1
> solution - Cenzic, the only one to win the Analyst's Choice Award from
> eWeek. As attacks through web applications continue to rise, you need to
> proactively protect your applications from hackers. Cenzic has the most
> comprehensive solutions to meet your application security penetration
> testing and vulnerability management needs. You have an option to go
> with a managed service (Cenzic ClickToSecure) or an enterprise software
> (Cenzic Hailstorm). Download FREE whitepaper on how a managed service
> can help you: http://www.cenzic.com/news_events/wpappsec.php And, now
> for a limited time we can do a FREE audit for you to confirm your
> results from other product. Contact us at request () cenzic com for details.
> ------------------------------------------------------------------------------
>
>
>

------------------------------------------------------------------------------
This List Sponsored by: Cenzic

Concerned about Web Application Security? Why not go with the #1 solution - Cenzic, the only one to win the Analyst's Choice Award from eWeek. As attacks through web applications continue to rise, you need to proactively protect your applications from hackers. Cenzic has the most comprehensive solutions to meet your application security penetration testing and vulnerability management needs. You have an option to go with a managed service (Cenzic ClickToSecure) or an enterprise software (Cenzic Hailstorm). Download FREE whitepaper on how a managed service can help you: http://www.cenzic.com/news_events/wpappsec.php And, now for a limited time we can do a FREE audit for you to confirm your results from other product. Contact us at request () cenzic com for details.
------------------------------------------------------------------------------


  By Date           By Thread  

Current thread:
[ Nmap | Sec Tools | Mailing Lists | Site News | About/Contact | Advertising | Privacy ]
AlienVault