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 Matching Modules ================ Name Disclosure Date Rank Description ---- --------------- ---- ----------- auxiliary/scanner/misc/oki_scanner normal OKI Printer Default Login Credential Scanner auxiliary/scanner/snmp/aix_version normal AIX SNMP Scanner Auxiliary Module auxiliary/scanner/snmp/cisco_config_tftp normal Cisco IOS SNMP Configuration Grabber (TFTP) auxiliary/scanner/snmp/cisco_upload_file normal Cisco IOS SNMP File Upload (TFTP) auxiliary/scanner/snmp/snmp_enum normal SNMP Enumeration Module auxiliary/scanner/snmp/snmp_enumshares normal SNMP Windows SMB Share Enumeration auxiliary/scanner/snmp/snmp_enumusers normal SNMP Windows Username Enumeration auxiliary/scanner/snmp/snmp_login normal SNMP Community Scanner auxiliary/scanner/snmp/snmp_set normal SNMP Set Module auxiliary/scanner/snmp/xerox_workcentre_enumusers normal Xerox WorkCentre User Enumeration (SNMP) exploit/windows/ftp/oracle9i_xdb_ftp_unlock 2003-08-18 great Oracle 9i XDB FTP UNLOCK Overflow (win32) exploit/windows/http/hp_nnm_ovwebsnmpsrv_main 2010-06-16 great HP OpenView Network Node Manager ovwebsnmpsrv.exe main Buffer Overflow exploit/windows/http/hp_nnm_ovwebsnmpsrv_ovutil 2010-06-16 great HP OpenView Network Node Manager ovwebsnmpsrv.exe ovutil Buffer Overflow exploit/windows/http/hp_nnm_ovwebsnmpsrv_uro 2010-06-08 great HP OpenView Network Node Manager ovwebsnmpsrv.exe Unrecognized Option Buffer Overflow exploit/windows/http/hp_nnm_snmp 2009-12-09 great HP OpenView Network Node Manager Snmp.exe CGI Buffer Overflow exploit/windows/http/hp_nnm_snmpviewer_actapp 2010-05-11 great HP OpenView Network Node Manager snmpviewer.exe Buffer Overflow post/windows/gather/enum_snmp normal Windows Gather SNMP Settings Enumeration (Registry) msf > use auxiliary/scanner/snmp/snmp_login msf auxiliary(snmp_login) > show options Module options (auxiliary/scanner/snmp/snmp_login): Name Current Setting Required Description ---- --------------- -------- ----------- BATCHSIZE 256 yes The number of hosts to probe in each set BLANK_PASSWORDS true no Try blank passwords for all users BRUTEFORCE_SPEED 5 yes How fast to bruteforce, from 0 to 5 CHOST no The local client address PASSWORD no The password to test PASS_FILE /usr/share/metasploit-framework/data/wordlists/snmp_default_pass.txt no File containing communities, one per line RHOSTS yes The target address range or CIDR identifier RPORT 161 yes The target port STOP_ON_SUCCESS false yes Stop guessing when a credential works for a host THREADS 1 yes The number of concurrent threads USER_AS_PASS true no Try the username as the password for all users VERBOSE true yes Whether to print output for all attempts msf auxiliary(snmp_login) > set RHOSTS 192.168.0.0-192.168.5.255 rhosts => 192.168.0.0-192.168.5.255 msf auxiliary(snmp_login) > set THREADS 10 threads => 10 msf auxiliary(snmp_login) > run [*] >> 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.
We can gather lots of information when using SNMP scanning modules. Such as open ports, services, hostname, processes and uptime to name a few. Using our Metasploitable virtual machine as our target, we'll run the 'snmp_enum' module and see what information it will provide us. First we load the module and set the RHOST option using the information stored in our workspace. Using hosts -R will set this options for us.
msf auxiliary(snmp_enum) > run [+] 172.16.194.172, Connected. [*] System information: Host IP : 172.16.194.172 Hostname : metasploitable Description : Linux metasploitable 2.6.24-16-server #1 SMP Thu Apr 10 13:58:00 UTC 2008 i686 Contact : email@example.com Location : Metasploit Lab Uptime snmp : 02:35:38.71 Uptime system : 00:20:13.21 System date : 2012-7-9 18:11:11.0 [*] Network information: IP forwarding enabled : no Default TTL : 64 TCP segments received : 19 TCP segments sent : 21 TCP segments retrans : 0 Input datagrams : 5055 Delivered datagrams : 5050 Output datagrams : 4527 ...snip... [*] Device information: Id Type Status Descr 768 Processor unknown GenuineIntel: Intel(R) Core(TM) i7-2860QM CPU @ 2.50GHz 1025 Network unknown network interface lo 1026 Network unknown network interface eth0 1552 Disk Storage unknown SCSI disk (/dev/sda) 3072 Coprocessor unknown Guessing that there's a floating point co-processor [*] Processes: Id Status Name Path Parameters 1 runnable init /sbin/init 2 runnable kthreadd kthreadd 3 runnable migration/0 migration/0 4 runnable ksoftirqd/0 ksoftirqd/0 5 runnable watchdog/0 watchdog/0 6 runnable events/0 events/0 7 runnable khelper khelper 41 runnable kblockd/0 kblockd/0 68 runnable kseriod kseriod ...snip... 5696 runnable su su 5697 runnable bash bash 5747 running snmpd snmpd [*] Scanned 1 of 1 hosts (100% complete) [*] Auxiliary module execution completed
The output provided by our scan provides us with a wealth of information on our system. Although cropped for length, we can still see lots of relavant information about our target such as processor type, process IDs etc.