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Re: nmap snmp scanning
From: Kent Hundley <khundley () opnet com>
Date: Tue, 06 Dec 2011 10:20:55 -0500

David,

Thanks much, you hit the nail on the head. For some reason, nmap was not using the file I was supplying with the snmp community strings. I tried using the snmp-brute script option and I noticed that if I supplied the snmpcommunities file option, nmap kept just using some default values. Looking at the snmp-brute.nse file, I found a section that specified a list of default communities to use and just substituted the string I wanted for one of the defaults and lo and behold the scan told me which string was in use.

After trying this I then went back and re-created the snmpcommunities.lst file in the root of the nmap dir and suddenly it started working. I'm not sure what the issue was originally, but its working now. For completeness and to help anyone else who has this issue, here is the exact command that is working now, the "snmpcommunities.lst" file is in the same dir as the nmap.exe (this is on Windows BTW):

C:\Program Files (x86)\Nmap>type snmpcommunities.lst
test

C:\Program Files (x86)\Nmap>nmap -sU -p161 --script snmp-brute 192.168.200.2 --s
cript-args snmplist=snmpcommunities.lst

Starting Nmap 5.51 ( http://nmap.org ) at 2011-12-06 09:42 Eastern Standard Time

Nmap scan report for 192.168.200.2
Host is up (0.012s latency).
PORT    STATE SERVICE
161/udp open  snmp
|_snmp-brute: test
MAC Address: CC:02:1B:80:00:00 (Unknown)

Nmap done: 1 IP address (1 host up) scanned in 2.35 seconds

C:\Program Files (x86)\Nmap>


Thanks,
Kent



On 12/5/2011 12:21 PM, David Fifield wrote:
On Mon, Dec 05, 2011 at 11:58:42AM -0500, Kent Hundley wrote:
David,

Thanks for your response, but this doesn't seem to resolve my issue.
If I run that command, it will tell me that the SNMP port is open,
but it doesn't tell me which of the available SNMP strings a given
device is using (I have 3 possible strings in community.lst).

The command and output are below. I tried putting the community.lst
file in the same dir as the nmap exe as well as in the nselib/data
dir where the other lst files are located. Interestingly, I get the
exact same response if I put a single bogus entry in the
community.lst file or even if I run the command without the
snmp-brute option at all. Its as if nmap is not reading the
community file at all.

D:\Program Files (x86)\Nmap>nmap -sU -p161 --script snmp-brute
--script-args snmplist=community.lst 10.x.y.z

Starting Nmap 5.51 ( http://nmap.org ) at 2011-12-05 16:46 GMT Standard Time
Nmap scan report for 10.x.y.z
Host is up (0.80s latency).
PORT    STATE SERVICE
161/udp open  snmp

Nmap done: 1 IP address (1 host up) scanned in 8.52 seconds
Try using the -d and --script-trace options. You may want to read some
more about how the script engine works at http://nmap.org/book/nse.html.

It's possible that the device is using none of the community strings in
community.lst. --script-trace will reveal what is going on.

David Fifield

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