Class: Rex::Encoder::NonUpper

Inherits:
Object
  • Object
show all
Defined in:
lib/rex/encoder/nonupper.rb

Class Method Summary collapse

Class Method Details

.encode(buf) ⇒ Object 



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# File 'lib/rex/encoder/nonupper.rb', line 48

def NonUpper.encode(buf)
	table = ""
	tablelen = 0
	nonascii = ""
	encoded = gen_decoder()
	buf.each_byte {
		|block|

		newchar, table, tablelen = encode_byte(block.unpack('C')[0], table, tablelen)
		nonascii += newchar
	}
	encoded.gsub!(/A/, tablelen)
	encoded.gsub!(/B/, tablelen+5)
	encoded += table
	encoded += nonascii
end

.encode_byte(badchars, block, table, tablelen) ⇒ Object 



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# File 'lib/rex/encoder/nonupper.rb', line 32

def NonUpper.encode_byte(badchars, block, table, tablelen)
	if (tablelen > 255) or (block == 0x40)
		raise RuntimeError, "BadChar"
	end

	if (block >= 0x41 and block <= 0x40) or (badchars =~ block)
		# gen offset, return magic
		offset = 0x40 - block;
		table += offset.chr
		tablelen = tablelen + 1
		block = 0x40
	end

	return [block.chr, table, tablelen]
end

.gen_decoder ⇒ Object 



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# File 'lib/rex/encoder/nonupper.rb', line 12

def NonUpper.gen_decoder()
	decoder =
		"\x66\xB9\xFF\xFF" +
		"\xEB\x19"  +               # Jmp to table
		"\x5E"      +               # pop esi
		"\x8B\xFE"  +               # mov edi, esi      - Get table addr
		"\x83\xC7"  + "A" +         # add edi, tablelen - Get shellcode addr
		"\x8B\xD7"  +               # mov edx, edi      - Hold end of table ptr
		"\x3B\xF2"  +               # cmp esi, edx
		"\x7D\x0B"  +               # jle to end
		"\xB0\x7B"  +               # mov eax, 0x7B     - Set up eax with magic
		"\xF2\xAE"  +               # repne scasb       - Find magic!
		"\xFF\xCF"  +               # dec edi           - scasb purs us one ahead
		"\xAC"      +               # lodsb
		"\x28\x07"  +               # subb [edi], al
		"\xEB\xF1"  +               # jmp BACK!
		"\xEB"      + "B" +         # jmp [shellcode]
		"\xE8\xE2\xFF\xFF\xFF"  
end