bcoles
102 lines
2.9 KiB
Ruby
102 lines
2.9 KiB
Ruby
##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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require 'rex/encoder/alpha2/alpha_upper'
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class MetasploitModule < Msf::Encoder::Alphanum
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Rank = LowRanking
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def initialize
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super(
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'Name' => 'Alpha2 Alphanumeric Uppercase Encoder',
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'Description' => %q{
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Encodes payloads as alphanumeric uppercase text. This encoder uses
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SkyLined's Alpha2 encoding suite.
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A pure alpha encoder is impossible without having a register that points at or near the shellcode.
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In a default configuration the first few bytes at the beginning are an fnstenv getpc stub (the same as used in shikata_ga_nai) and thus are not alphanumeric.
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You can set BufferRegister for full alpha (see Encoder options for details).
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},
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'Author' => [ 'pusscat', 'skylined' ],
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'Arch' => ARCH_X86,
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'License' => BSD_LICENSE,
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'EncoderType' => Msf::Encoder::Type::AlphanumUpper,
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'Decoder' => {
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'BlockSize' => 1
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})
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end
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#
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# Returns the decoder stub that is adjusted for the size of the buffer
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# being encoded.
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#
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def decoder_stub(state)
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modified_registers = []
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reg = datastore['BufferRegister']
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off = (datastore['BufferOffset'] || 0).to_i
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buf = ''
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# We need to create a GetEIP stub for the exploit
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if !reg
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if datastore['AllowWin32SEH'] && datastore['AllowWin32SEH'].to_s =~ (/^(t|y|1)/i)
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buf = 'VTX630WTX638VXH49HHHPVX5AAQQPVX5YYYYP5YYYD5KKYAPTTX638TDDNVDDX4Z4A63861816'
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reg = 'ECX'
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off = 0
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modified_registers.concat(
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[
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Rex::Arch::X86::ESP,
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Rex::Arch::X86::EDI,
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Rex::Arch::X86::ESI,
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Rex::Arch::X86::EAX
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]
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)
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else
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res = Rex::Arch::X86.geteip_fpu(state.badchars, modified_registers)
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if !res
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raise EncodingError, 'Unable to generate geteip code'
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end
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buf, reg, off = res
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end
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else
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reg.upcase!
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end
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stub = buf + Rex::Encoder::Alpha2::AlphaUpper.gen_decoder(reg, off, modified_registers)
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# Sanity check that saved_registers doesn't overlap with modified_registers
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modified_registers.uniq!
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if !(modified_registers & saved_registers).empty?
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raise BadGenerateError
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end
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stub
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end
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#
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# Encodes a one byte block with the current index of the length of the
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# payload.
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#
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def encode_block(state, block)
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return Rex::Encoder::Alpha2::AlphaUpper.encode_byte(block.unpack('C')[0], state.badchars)
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end
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#
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# Tack on our terminator
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#
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def encode_end(state)
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state.encoded += Rex::Encoder::Alpha2::AlphaUpper.add_terminator
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end
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# Indicate that this module can preserve some registers
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def can_preserve_registers?
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true
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end
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# Convert the SaveRegisters to an array of x86 register constants
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def saved_registers
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Rex::Arch::X86.register_names_to_ids(datastore['SaveRegisters'])
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end
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end
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