285 lines
6.0 KiB
Ruby
285 lines
6.0 KiB
Ruby
require 'msf/core'
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module Msf
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###
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#
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# EncoderState
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# ------------
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#
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# This class is used to track the state of a single encoding operation
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# from start to finish.
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#
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###
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class EncoderState
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def initialize(key = nil)
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reset(key)
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end
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# Reset the encoder state
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def reset(key = nil)
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init_key(key)
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self.encoded = ''
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end
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# Set the initial encoding key
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def init_key(key)
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self.key = key
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self.orig_key = key
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end
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attr_accessor :key
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attr_accessor :orig_key
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attr_accessor :encoded
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attr_accessor :context
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attr_accessor :badchars
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attr_accessor :buf
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# Decoder settings
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attr_accessor :decoder_key_offset, :decoder_key_size, :decoder_key_pack
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end
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###
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#
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# Encoder
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# -------
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#
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# This class is the base class that all encoders inherit from.
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#
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###
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class Encoder < Module
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def initialize(info)
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super(info)
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end
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#
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# Encoder information accessors that can be overriden
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# by derived classes
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#
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def type
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return MODULE_ENCODER
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end
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#
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# Returns the decoder stub to use based on the supplied length
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#
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def decoder_stub(state)
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return module_info['Decoder']['Stub']
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end
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def decoder_key_offset
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return module_info['Decoder']['KeyOffset']
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end
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def decoder_key_size
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return module_info['Decoder']['KeySize']
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end
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def decoder_block_size
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return module_info['Decoder']['BlockSize']
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end
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def decoder_key_pack
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return module_info['Decoder']['KeyPack'] || 'V'
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end
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#
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# Encoding
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#
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def encode(buf, badchars, state = nil)
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# Initialize an empty set of bad characters
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badchars = '' if (!badchars)
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# Initialize the encoding state and key as necessary
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if (state == nil)
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state = EncoderState.new
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end
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# Prepend data to the buffer as necessary
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buf = prepend_buf + buf
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# If this encoder is key-based and we don't already have a key, find one
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if ((decoder_key_size) and
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(state.key == nil))
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# Find a key that doesn't contain and wont generate any bad
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# characters
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state.init_key(find_key(buf, badchars))
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if (state.key == nil)
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raise NoKeyError, "A key could not be found for the #{self.name} encoder.", caller
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end
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end
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# Update the state with default decoder information
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state.decoder_key_offset = decoder_key_offset
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state.decoder_key_size = decoder_key_size
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state.decoder_key_pack = decoder_key_pack
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# Save the buffer in the encoding state
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state.badchars = badchars
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state.buf = buf
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# Call encode_begin to do any encoder specific pre-processing
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encode_begin(state)
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# Perform the actual encoding operation with the determined state
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do_encode(buf, badchars, state)
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# Call encoded_end to do any encoder specific post-processing
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encode_end(state)
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# Return the encoded buffer to the caller
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return state.encoded
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end
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def do_encode(buf, badchars, state)
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# Copy the decoder stub since we may need to modify it
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stub = decoder_stub(state).dup
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if (state.key != nil)
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# Substitute the decoder key in the copy of the decoder stub with the
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# one that we found
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stub[state.decoder_key_offset,state.decoder_key_size] = [ state.key.to_i ].pack(state.decoder_key_pack)
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end
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# Walk the buffer encoding each block along the way
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offset = 0
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while (offset < buf.length)
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block = buf[offset, decoder_block_size]
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state.encoded += encode_block(state,
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block + ("\x00" * (decoder_block_size - block.length)))
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offset += decoder_block_size
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end
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# Prefix the decoder stub to the encoded buffer
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state.encoded = stub + state.encoded
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# Last but not least, do one last badchar pass to see if the stub +
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# encoded payload leads to any bad char issues...
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if ((badchar_idx = has_badchars?(state.encoded, badchars)) != nil)
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raise BadcharError.new(state.encoded, badchar_idx, stub.length, badchars[badchar_idx]),
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"The #{self.name} encoder failed to encode without bad characters.",
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caller
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end
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return true
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end
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#
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# Buffer management
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#
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def prepend_buf
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return ''
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end
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#
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# Pre-processing, post-processing, and block encoding stubs
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#
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def encode_begin(state)
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return nil
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end
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def encode_end(state)
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return nil
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end
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def encode_block(state, block)
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return block
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end
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protected
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def find_key(buf, badchars)
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key_bytes = [ ]
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cur_key = [ ]
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bad_keys = find_bad_keys(buf, badchars)
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found = false
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# Keep chugging until we find something...right
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while (!found)
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# Scan each byte position
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0.upto(decoder_key_size - 1) { |index|
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cur_key[index] = rand(255)
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# Scan all 255 bytes (wrapping around as necessary)
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for cur_char in (cur_key[index] .. (cur_key[index] + 255))
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cur_char = (cur_char % 255) + 1
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# If this is a known bad character at this location in the
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# key or it doesn't pass the bad character check...
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if (((bad_keys != nil) and
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(bad_keys[index][cur_char] == true)) or
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(badchars.index(cur_char) != nil))
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next
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end
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key_bytes[index] = cur_char
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end
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}
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# Assume that we're going to rock this shit...
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found = true
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# Scan each byte and see what we've got going on to make sure
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# no funny business is happening
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key_bytes.each { |byte|
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if (badchars.index(byte) != nil)
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found = false
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end
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}
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end
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# Do we have all the key bytes accounted for?
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if (key_bytes.length != decoder_key_size)
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return nil
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end
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return key_bytes_to_integer(key_bytes)
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end
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def find_bad_keys
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return [ {}, {}, {}, {} ]
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end
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def has_badchars?(buf, badchars)
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badchars.each_byte { |badchar|
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idx = buf.index(badchar)
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if (idx != nil)
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return idx
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end
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}
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return nil
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end
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# Convert individual key bytes into a single integer based on the
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# decoder's key size and packing requirements
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def key_bytes_to_integer(key_bytes)
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return key_bytes.pack('C' + decoder_key_size.to_s).unpack(decoder_key_pack)[0]
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end
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# Convert an integer into the individual key bytes based on the
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# decoder's key size and packing requirements
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def integer_to_key_bytes(integer)
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return [ integer.to_i ].pack(decoder_key_pack).unpack('C' + decoder_key_size.to_s)
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end
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end
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end
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require 'msf/core/encoder/xor'
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require 'msf/core/encoder/xor_additive_feedback'
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