Penetration Testing: Re: nmap showing port 21 (ftp) open, but port is actually closed

[Andres Riancho <andres.riancho () gmail com>]

Mike,

   This could be a transparent proxy server that your ISP installed.

   A way to test if you are proxyed is:

gauss:~# tcptraceroute www.google.com 80
Selected device eth1, address 24.232.100.167, port 3539 for outgoing packets
Tracing the path to www.google.com (64.233.161.99) on TCP port 80 (www), 
30 hops max
1  * 10.17.1.1 7.865 ms *
2  10.101.1.25  10.882 ms  13.205 ms  7.474 ms
3  publica1.fibertel.com.ar (24.232.1.1)  7.483 ms  5.732 ms  8.831 ms
4  64.233.161.99 [open]  7.639 ms  32.874 ms  13.350 ms

Only 4 hops for port 80. Strange ...
Lets see what happends for real...

gauss:~#traceroute 64.233.161.99
traceroute to 64.233.161.99 (64.233.161.99), 30 hops max, 38 byte packets
1  * * *
2  10.101.1.25 (10.101.1.25)  10.071 ms  8.694 ms  28.814 ms
3  publica1.fibertel.com.ar (24.232.1.1)  7.851 ms  26.046 ms  11.893 ms
4  10.101.21.85 (10.101.21.85)  11.420 ms  21.271 ms  8.380 ms
5  bai1-cablevision-1-ar.bai.seabone.net (195.22.220.45)  7.919 ms  
9.622 ms  20.910 ms
6  ash1-new1-racc1.new.seabone.net (195.22.216.169)  188.225 ms  
198.841 ms  183.207 ms
7  eqixva-google-gige.google.com (206.223.115.21)  184.185 ms  183.390 
ms  201.727 ms
8  216.239.47.120 (216.239.47.120)  186.700 ms  183.013 ms 
216.239.49.248 (216.239.49.248)  183.718 ms
9  216.239.48.190 (216.239.48.190)  186.032 ms  184.994 ms 
216.239.48.198 (216.239.48.198)  183.713 ms
10  64.233.161.99 (64.233.161.99)  183.273 ms  184.863 ms  186.683 ms

Well, this makes more sense to me :) . You could do the same test but 
changing port 80 to 21.
Mike Jones wrote:

> Has anyone ever seen this before, nmap is showing port 21 to be open 
> on a machine on the internet, but 21 is not listening on that 
> machine.  It happens to all machines I scan outside the local area 
> network.
> Thanks in advance
--
Andrés Riancho

http://www.securearg.net/
Secure from the Source


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